Add server implementation for FindRemoteRootRef
What does this MR do?
Queries the remote to determine its HEAD. Parsing the HEAD from git remote show <remote> is brittle, but there is no other way for now. In the future, we expect to have a new --update-head option in git fetch see https://gitlab.com/gitlab-org/gitlab-ee/issues/7211#note_94821436.
What are the relevant issue numbers?
Edited by GitLab Release Tools Bot