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.