[cognito] Cognito standalone

[charlesg3]

Description of changes:
Add support for providing an external cognito.

Standalone Cognito

• https://eu-west-1.console.aws.amazon.com/cloudformation/home?region=eu-west-1#/stacks/quickcreate?stackName=cognito-standalone&templateURL=https://pcluster-manager-eu-west-1.s3.eu-west-1.amazonaws.com/cognito-standalone.yaml

ParallelCluster Manager Stack that consumes it:

• https://eu-west-1.console.aws.amazon.com/cloudformation/home?region=eu-west-1#/stacks/create/review?stackName=pcluster-manager&templateURL=https://pcluster-manager-eu-west-1.s3.eu-west-1.amazonaws.com/pcluster-manager.yaml

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[sean-smith]

I got an email with the temporary password before the stack finished creating. The email didn't include the login link.

Did we somehow break that feature?

[charlesg3]

I got an email with the temporary password before the stack finished creating. The email didn't include the login link.

Did we somehow break that feature?

No -- if the cognito is created external, it doesn't know which stack you're referring to so it doesn't have that link. If you don't specify the external cognito then it will be created as a part of the PCM stack and the login link will be sent as before.

[mtfranchetto]

Closing in favor of #459