feat(cognito): support UserPoolGroup (#31351)

### Issue # (if applicable)

Closes #21026.

### Reason for this change
To support UserPool Group L2 Construct.


### Description of changes
Add `UserPoolGroup` class.



### Description of how you validated changes
Add unit tests and integ tests.


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: mazyu36