Feature: bring your own UserPool

[bogdankatishev]

Description of changes: Added new CfnParameter: ExistingCognitoPoolId:

• If empty string is passed (""): it will create a DLTUserPool Resource.
• If an Cognito PoolId is passed: it will skip the creation of the DLTUserPool Resource and it will use your own given UserPool.

Also updated the snapshots and tests of the templates to includes these changes :arrow_up:

Checklist

• [x] :wave: I have run the unit tests, and all unit tests have passed.
• [ ] :warning: This pull request might incur a breaking change.

A question towards the people of AWS/maintainers: should I include a Condition to skip the creation of the default admin user when giving an existing Cognito PoolId?

[kamyarz-aws]

Thank you for this contribution. We will review this feature with our product team and if approved internally we will include this in one of our future releases with your name as a contributor.

[kamyarz-aws]

Hi @bogdankatishev, can you please gives some more information on why do you want to include this feature. I understand the logic but I also want to know more how different users might use this feature.

[bogdankatishev]

Hello @kamyarz-aws, I added this feature because we already had an existing Cognito UserPool within our AWS account where all the existing system accounts/etc... reside. And so we wanted to avoid creating a new UserPool, with only 1 default system user in it.