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/controllers/projects/git_http_client_controller.rb

@@ -79,7 +79,7 @@ def project
   end
 
   def parse_repo_path
-    @project, @repo_type, @redirected_path, @suffix = Gitlab::RepoPath.parse("#{params[:namespace_id]}/#{params[:project_id]}")
+    @project, @repo_type, @redirected_path, @subject_id = Gitlab::RepoPath.parse("#{params[:namespace_id]}/#{params[:repository_id]}")
   end
 
   def render_missing_personal_access_token
@@ -90,25 +90,16 @@ def render_missing_personal_access_token
   end
 
   def repository
-    render_404 if snippet? && !snippet
+    return if repo_type.snippet? && !snippet
 
     repo_type.repository_for(snippet || project)
   end
 
-  def wiki?
-    repo_type.wiki?
-  end
-
-  def snippet?
-    repo_type.snippet?
-  end
-
   def snippet
     strong_memoize(:snippet) do
-      next unless snippet?
+      next unless repo_type.snippet?
 
-      snippet_id = repo_type.fetch_id(@suffix)
-      project&.snippets&.find_by_id(snippet_id)
+      project&.snippets&.find_by_id(@subject_id)
       # SnippetsFinder.new(authenticated_user, project: project, ids: snippet_id).execute.first
     end
   end