[11.6 EE] Backport Rugged implementations for Git access

Due to performance issues over NFS, GitLab 11.9 shipped with feature flag that brings back Rugged implementations for certain Gitaly calls: https://docs.gitlab.com/ee/administration/high_availability/nfs.html#improving-nfs-performance-with-gitlab.

A number of customers are using 11.5 - 11.8 and may be hesitant to make the leap to 11.9. This merge request backports these fixes to 11.6.

https://gitlab.com/gitlab-org/gitlab-ce/issues/57317 describes the issue in detail. These merge requests were backported:

• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25477
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25702
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25706
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25674
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25896
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26813
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27441

Related to gitlab-org/release/tasks#749 (closed)

CE port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27536