Finish implementation of "delete user"

[amberrignell]

@elias-ba has confirmed that in resolution of this issue he will handle every user relation in the app:

• credential.user_id
• invocation_reason.user_id
• project_user.user_id

Initial bug report

Describe the bug
Every day, we check for users that have been scheduled for deletion and delete users. The oban job is running ok, but the command is failing because of database constraints which means that users that should be deleted aren't

Version number v0.4.6
I have reproduced this locally on main:

• Yes
• No

To Reproduce

1. In runtime.exs, update line 39 to check users for deletion every minute {"* * * * *", Lightning.Accounts, args: %{"type" => "purge_deleted"}},
2. Run Lightning
3. Log in as a superuser
4. Delete a user
5. Edit the scheduled for deletion time to 1 minute from now
6. Wait one minute
7. See user is not deleted and there is an error in the terminal (stack trace posted below)

Expected behaviour
The user should be deleted and removed from any project they are part of.
When a user is scheduled for deletion, check if any of their resources (ex: credentials) are being used in existing projects.

Additional context

Stack trace below:

[error] Oban exception:
%RuntimeError{message: "you are attempting to change relation :project_users of\nLightning.Projects.Project but the `:on_replace` option of this relation\nis set to `:raise`.\n\nBy default it is not possible to replace or delete embeds and\nassociations during `cast`. Therefore Ecto requires the parameters\ngiven to `cast` to have IDs matching the data currently associated\nto Lightning.Projects.Project. Failing to do so results in this error message.\n\nIf you want to replace data or automatically delete any data\nnot sent to `cast`, please set the appropriate `:on_replace`\noption when defining the relation. The docs for `Ecto.Changeset`\ncovers the supported options in the \"Associations, embeds and on\nreplace\" section.\n\nHowever, if you don't want to allow data to be replaced or\ndeleted, only updated, make sure that:\n\n  * If you are attempting to update an existing entry, you\n    are including the entry primary key (ID) in the data.\n\n  * If you have a relationship with many children, all children\n    must be given on update.\n\n"}
    (ecto 3.9.4) lib/ecto/changeset/relation.ex:238: Ecto.Changeset.Relation.on_replace/2
    (ecto 3.9.4) lib/ecto/changeset/relation.ex:409: Ecto.Changeset.Relation.reduce_delete_changesets/5
    (ecto 3.9.4) lib/ecto/changeset/relation.ex:121: Ecto.Changeset.Relation.cast/5
    (ecto 3.9.4) lib/ecto/changeset.ex:832: Ecto.Changeset.cast_relation/4
    (lightning 0.4.6) lib/lightning/projects/project.ex:37: Lightning.Projects.Project.changeset/2
    (lightning 0.4.6) lib/lightning/projects.ex:112: Lightning.Projects.update_project/2
    (elixir 1.14.2) lib/enum.ex:975: Enum."-each/2-lists^foreach/1-0-"/2
    (lightning 0.4.6) lib/lightning/accounts.ex:34: Lightning.Accounts.purge_user/1
    (elixir 1.14.2) lib/enum.ex:975: Enum."-each/2-lists^foreach/1-0-"/2
    (lightning 0.4.6) lib/lightning/accounts.ex:76: Lightning.Accounts.perform/1
    (oban 2.14.2) lib/oban/queue/executor.ex:129: Oban.Queue.Executor.perform/1
    (oban 2.14.2) lib/oban/queue/executor.ex:74: Oban.Queue.Executor.call/1
    (elixir 1.14.2) lib/task/supervised.ex:89: Task.Supervised.invoke_mfa/2
    (elixir 1.14.2) lib/task/supervised.ex:34: Task.Supervised.reply/4
    (stdlib 4.2) proc_lib.erl:240: :proc_lib.init_p_do_apply/3

meta:
  %{
  args: %{"type" => "purge_deleted"},
  attempt: 1,
  conf: %Oban.Config{
    dispatch_cooldown: 100,
    engine: Oban.Engines.Basic,
    get_dynamic_repo: nil,
    log: false,
    name: Oban,
    node: "ambers-MacBook-Air",
    notifier: Oban.Notifiers.Postgres,
    peer: Oban.Peers.Postgres,
    plugins: [
      {Oban.Plugins.Cron,
       [
         crontab: [
           {"* * * * *", Lightning.Jobs.Scheduler},
           {"* * * * *", ObanPruner},
           {"* * * * *", Lightning.Accounts,
            [args: %{"type" => "purge_deleted"}]},
           {"0 10 * * *", Lightning.DigestEmailWorker,
            [args: %{"type" => "daily_project_digest"}]},
           {"0 10 * * MON", Lightning.DigestEmailWorker,
            [args: %{"type" => "weekly_project_digest"}]},
           {"0 10 1 * *", Lightning.DigestEmailWorker,
            [args: %{"type" => "monthly_project_digest"}]}
         ]
       ]}
    ],
    prefix: "public",
    queues: [
      scheduler: [limit: 1],
      workflow_failures: [limit: 1],
      background: [limit: 1],
      runs: [limit: 4]
    ],
    repo: Lightning.Repo,
    shutdown_grace_period: 60000,
    stage_interval: 1000,
    testing: :disabled
  },
  id: 8224,
  job: %Oban.Job{
    __meta__: #Ecto.Schema.Metadata<:loaded, "public", "oban_jobs">,
    id: 8224,
    state: "executing",
    queue: "background",
    worker: "Lightning.Accounts",
    args: %{"type" => "purge_deleted"},
    meta: %{},
    tags: [],
    errors: [],
    attempt: 1,
    attempted_by: ["ambers-MacBook-Air"],
    max_attempts: 1,
    priority: 0,
    attempted_at: ~U[2023-03-29 09:18:00.289256Z],
    cancelled_at: nil,
    completed_at: nil,
    discarded_at: nil,
    inserted_at: ~U[2023-03-29 09:18:00.026985Z],
    scheduled_at: ~U[2023-03-29 09:18:00.026985Z],
    conf: %Oban.Config{
      dispatch_cooldown: 100,
      engine: Oban.Engines.Basic,
      get_dynamic_repo: nil,
      log: false,
      name: Oban,
      node: "ambers-MacBook-Air",
      notifier: Oban.Notifiers.Postgres,
      peer: Oban.Peers.Postgres,
      plugins: [
        {Oban.Plugins.Cron,
         [
           crontab: [
             {"* * * * *", Lightning.Jobs.Scheduler},
             {"* * * * *", ObanPruner},
             {"* * * * *", Lightning.Accounts,
              [args: %{"type" => "purge_deleted"}]},
             {"0 10 * * *", Lightning.DigestEmailWorker,
              [args: %{"type" => "daily_project_digest"}]},
             {"0 10 * * MON", Lightning.DigestEmailWorker,
              [args: %{"type" => "weekly_project_digest"}]},
             {"0 10 1 * *", Lightning.DigestEmailWorker,
              [args: %{"type" => "monthly_project_digest"}]}
           ]
         ]}
      ],
      prefix: "public",
      queues: [
        scheduler: [limit: 1],
        workflow_failures: [limit: 1],
        background: [limit: 1],
        runs: [limit: 4]
      ],
      repo: Lightning.Repo,
      shutdown_grace_period: 60000,
      stage_interval: 1000,
      testing: :disabled
    },
    conflict?: false,
    replace: nil,
    unique: nil,
    unsaved_error: %{
      kind: :error,
      reason: %RuntimeError{
        message: "you are attempting to change relation :project_users of\nLightning.Projects.Project but the `:on_replace` option of this relation\nis set to `:raise`.\n\nBy default it is not possible to replace or delete embeds and\nassociations during `cast`. Therefore Ecto requires the parameters\ngiven to `cast` to have IDs matching the data currently associated\nto Lightning.Projects.Project. Failing to do so results in this error message.\n\nIf you want to replace data or automatically delete any data\nnot sent to `cast`, please set the appropriate `:on_replace`\noption when defining the relation. The docs for `Ecto.Changeset`\ncovers the supported options in the \"Associations, embeds and on\nreplace\" section.\n\nHowever, if you don't want to allow data to be replaced or\ndeleted, only updated, make sure that:\n\n  * If you are attempting to update an existing entry, you\n    are including the entry primary key (ID) in the data.\n\n  * If you have a relationship with many children, all children\n    must be given on update.\n\n"
      },
      stacktrace: [
        {Ecto.Changeset.Relation, :on_replace, 2,
         [
           file: 'lib/ecto/changeset/relation.ex',
           line: 238,
           error_info: %{module: Exception}
         ]},
        {Ecto.Changeset.Relation, :reduce_delete_changesets, 5,
         [file: 'lib/ecto/changeset/relation.ex', line: 409]},
        {Ecto.Changeset.Relation, :cast, 5,
         [file: 'lib/ecto/changeset/relation.ex', line: 121]},
        {Ecto.Changeset, :cast_relation, 4,
         [file: 'lib/ecto/changeset.ex', line: 832]},
        {Lightning.Projects.Project, :changeset, 2,
         [file: 'lib/lightning/projects/project.ex', line: 37]},
        {Lightning.Projects, :update_project, 2,
         [file: 'lib/lightning/projects.ex', line: 112]},
        {Enum, :"-each/2-lists^foreach/1-0-", 2,
         [file: 'lib/enum.ex', line: 975]},
        {Lightning.Accounts, :purge_user, 1,
         [file: 'lib/lightning/accounts.ex', line: 34]},
        {Enum, :"-each/2-lists^foreach/1-0-", 2,
         [file: 'lib/enum.ex', line: 975]},
        {Lightning.Accounts, :perform, 1,
         [file: 'lib/lightning/accounts.ex', line: 76]},
        {Oban.Queue.Executor, :perform, 1,
         [file: 'lib/oban/queue/executor.ex', line: 129]},
        {Oban.Queue.Executor, :call, 1,
         [file: 'lib/oban/queue/executor.ex', line: 74]},
        {Task.Supervised, :invoke_mfa, 2, [file: 'lib/task/supervised.ex', ...]},
        {Task.Supervised, :reply, 4, [...]},
        {:proc_lib, :init_p_do_apply, 3, ...}
      ]
    }
  },
  kind: :error,
  max_attempts: 1, (truncated)