Support for `skinny_users` endpoints

[codylittle]

Describe the feature request?

Given that the skinny_users endpoints for both group users and app users is the recommended best practice, native support for these would be excellent.

New or Affected Resource(s)

/api/v1/groups/{id}/skinny_users
/api/v1/apps/{id}/skinny_users

Provide a documentation link

No response

Additional Information?

No response

[github-actions]

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