Bring back Rugged implementation of ListCommitsByOid
This brings back changes in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20432.
For users using Gitaly on top of NFS, accessing the Git data directly via Rugged may be faster than going through than Gitaly. This merge request introduces the feature flag
rugged_list_commits_by_oid to activate the Rugged method.
For one customer, we saw that
ListCommitsByOid was the second highest used endpoint that may be causing increased load.