redshift: Redshift User Groups

### Describe the feature

Add an API for creating Redshift User Groups

### Use Case

Sometimes, infra developers may not need to create individual users, but entire groups, and then manage and maintain access to these groups through the Redshift Console.
If there are a vast number of users within a Redshift Data Warehouse, managing them within a single CDK application may be cumbersome, so these can be managed through a minimal amount of user groups, which can then be managed through the Redshift console, etc.

### Proposed Solution

Add a separate API within the Redshift Construct to access and maintain a group of `Redshift.User`. The Redshift Data API allows the execution of SQL code, which also includes the addition of running `GROUP` commands. Therefore, we can manage and maintain through the existing Redshift Data API already set up.

### Other Information

I am currently working on this, and it seems there will be a need to refactor the `UserTablePrivileges` internal construct, which I can create a separate `refactor` PR for.

### Acknowledgements

- [X] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2.76.0

### Environment details (OS name and version, etc.)

Amazon Linux 2

Start with the existing Redshift construct and its configured Redshift Data API, then inspect the UserTablePrivileges internal construct mentioned in the issue. The work is complete when the construct exposes an API for creating and maintaining Redshift user groups through the existing Data API, with appropriate tests added.

Written by the indexing model from the issue text.