Add `simple` attribute to group details endpoint

Zendesk: https://gitlab.zendesk.com/agent/tickets/51953

The List Projects API endpoint has a simple boolean attribute that will instruct the endpoint to only return each project's ID, URL, name, and path. A customer requests that we add this same attribute to the List a group's projects endpoint.

This seems like it will probably be fairly simple as we can re-use what's already there for the mentioned project endpoint.