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

@@ -279,7 +279,7 @@ def archive_metadata(ref, storage_path, format = "tar.gz", append_sha:, path: ni
     raw_repository.archive_metadata(
       ref,
       storage_path,
-      project.path,
+      project&.path,
       format,
       append_sha: append_sha,
       path: path
@@ -451,7 +451,7 @@ def after_import
     # It can be reenabled for specific tests via:
     #
     # allow(DetectRepositoryLanguagesWorker).to receive(:perform_async).and_call_original
-    DetectRepositoryLanguagesWorker.perform_async(project.id)
+    DetectRepositoryLanguagesWorker.perform_async(project.id) if project
   end
 
   # Runs code after a new commit has been pushed.
@@ -958,6 +958,7 @@ def fetch_as_mirror(url, forced: false, refmap: :all_refs, remote_name: nil, pru
   # rubocop:disable Gitlab/RailsLogger
   def async_remove_remote(remote_name)
     return unless remote_name
+    return unless project
 
     job_id = RepositoryRemoveRemoteWorker.perform_async(project.id, remote_name)