Add routes to allow git actions on snippet repositories

What does this MR do?

In this MR we implement the following:

• Refactors the git_http routes because, for now, snippet repositories won't support LFS (mainly because lfs_enabled is a project feature and we have to think if we could enable it by default for personal snippets).
• It also updates the GitHttpController(s) and the SSH internal API to allow basic cloning/pushing/pulling operations for resources other than projects.

Refs #39176 (closed) Closes #205666 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

app/models/repository.rb

@@ -1134,7 +1134,10 @@ def blobs_metadata(paths, ref = 'HEAD')
   end
 
   def project
-    repositorable
+    return repositorable if repositorable.is_a?(Project)
+    return unless repositorable.class.reflect_on_association(:project)
+
+    repositorable.project
   end
 
   private