mergiraf: init module

[bobvanderlinden]

Description

This adds git integration for mergiraf. It sets up git to use mergiraf to automatically resolve merge conflicts. See https://mergiraf.org/usage.html#registration-as-a-git-merge-driver

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all
  or nix build --reference-lock-file flake.lock ./tests#test-all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

[bobvanderlinden]

This is something I'm unsure of. Right now, it'll conflict if someone has set programs.git.attributes. It does update all language settings automatically.

Alternative 1: hard-coding the languages into programs.git.attributes, but we need to keep this list up-to-date, which is less than ideal.

Alternative 2: using mkDefault, but this will likely unintendedly remove the core mergiraf configuration.

Alternative 3: allowing programs.git.attributes to also include other files and concat it all. This will add somewhat complex functionality to the git module, so I'm unsure whether this is wanted for now.

[bobvanderlinden]

Ping @wetneb, this adds integration for mergiraf into home-manager, so that users can simply enable programs.mergiraf.enable = true; and have the merge config and attributes be setup and be updated automatically.

[bobvanderlinden]

I'm unsure why the test for macos is failing. The package name @mergiraf@ isn't being used and instead /nix/store/* is used somehow 😕

Any suggestions?