QuerySets: refactor _add_user_repos (#8182)
Get ready for sharing more code,
mainly rename `_add_user_repos` to `_add_from_user_projects` and
`_add_user_projects`.
Stat accepting admin and member attributes,
these aren't used here yet, but they will.
I have removed some overrides that weren't needed or weren't overridden
in .com.
