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/repositories/git_http_client_controller.rb

@@ -51,7 +51,6 @@ def authenticate_user
           return # Allow access
         end
       elsif http_download_allowed?
-
         @authentication_result = Gitlab::Auth::Result.new(nil, project, :none, [:download_code])
 
         return # Allow access
@@ -81,7 +80,7 @@ def project
     end
 
     def parse_repo_path
-      @project, @repo_type, @redirected_path = Gitlab::RepoPath.parse("#{params[:namespace_id]}/#{params[:repository_id]}")
+      @container, @project, @repo_type, @redirected_path = Gitlab::RepoPath.parse("#{params[:namespace_id]}/#{params[:repository_id]}")
     end
 
     def render_missing_personal_access_token
@@ -93,7 +92,7 @@ def render_missing_personal_access_token
 
     def repository
       strong_memoize(:repository) do
-        repo_type.repository_for(project)
+        repo_type.repository_for(@container)
       end
     end
 
@@ -117,7 +116,7 @@ def ci?
     def http_download_allowed?
       Gitlab::ProtocolAccess.allowed?('http') &&
       download_request? &&
-      project && Guest.can?(:download_code, project)
+      (project && Guest.can?(:download_code, project) || @container.is_a?(PersonalSnippet))
     end
   end
 end