Bring back Rugged implementation of find_commit
This brings back some of the changes in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20339.
For users using Gitaly on top of NFS, accessing the Git data directly via Rugged is more performant than Gitaly. This merge request introduces a feature flag
rugged_find_commit to activate Rugged implementation for the Gitaly
Part of four Rugged changes identified in https://gitlab.com/gitlab-org/gitlab-ce/issues/57317.