Create and Enpoint to Provide list of USER DEFINED repo Groups and Repos in them

> [!NOTE]
> Migrated from [augurlabs/augur#2558](https://github.com/augurlabs/augur/issues/2558)
> Originally opened by `@sgoggins` on 2023-10-25

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When users define groups, allow them to access a list of those groups, and the repositories in them using a repository and an API Key.

Start by locating the existing user-defined group and repository models or endpoints, then read how repository and API-key authentication is handled. Add an endpoint that returns a user's defined groups and the repositories in each, and verify that access is limited to the authenticated user.

Written by the indexing model from the issue text.