Bring back Rugged implementation of GetTreeEntries
This brings back some of the changes in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20343.
For users using Gitaly on top of NFS, accessing the Git data directly
via Rugged is more performant than Gitaly. This merge request introduces
the feature flag rugged_tree_entries
to activate the Rugged method.
Part of four Rugged changes identified in https://gitlab.com/gitlab-org/gitlab-ce/issues/57317.
Edited by Stan Hu