Copy LFS objects when a repository is pull mirrored

What does this MR do?

Copies LFS objects into the repository when it is pull mirrored.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/10871

app/helpers/mirror_helper.rb

@@ -7,6 +7,10 @@ module MirrorHelper
       project_mirror_endpoint: project_mirror_path(@project, :json)
     }
   end
+
+  def mirror_lfs_sync_message
+    _('The Git LFS objects will <strong>not</strong> be synced.').html_safe
+  end
 end
 
 MirrorHelper.prepend(EE::MirrorHelper)