Accept more paths as Git HTTP

Summary

With the introduction of group wikis we also need to support repository paths on the toplevel.

Related to gitlab#294007 (closed).

Background

This reintroduces the changes from !670 (merged), which were reverted in !681 (merged) because they were causing issues with old Git clients: gitlab-com/gl-infra/production#3387 (closed)

The problem was that we were only handling /info/refs Git HTTP requests in Workhorse if they had a valid service parameter. Otherwise they would be forwarded to Rails without the necessary JWT token, and caused an exception there.

So now we're back to forwarding all GET requests to a path ending in /info/refs, and let Rails deal with the missing service parameter as we did before. In that case Rails returns either a 401 or 403 response, depending on whether the user was authenticated or not. This behaviour is now verified on the Rails side in gitlab!53977 (merged).