collab: Route `UserService::get_user_by_github_login` through Cloud (#56190)

This PR makes it so we route the `UserService::get_user_by_github_login`
call through Cloud instead of hitting the database.

Closes CLO-743.

Release Notes:

- N/A
6b7d20efdbMarshall Bowers committed on 5/8/2026, 4:21:09 PM· committed by GitHubparentdc06395
2 files changedLine totals unavailable