Improve performance of GPG status badge on repository / tree / project overview / blob page
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20524 displays the GPG status on repository / tree / project overview / blob page by using the existing internal API endpoint to load all signatures on a branch. For those pages we only need the GPG signature for a single commit. Reducing this request should gain us a small performance improvement on those pages.