Why and how to enable this is covered in the docs being changed
here. This requires gitlab-org/gitlab-shell@2e8b670 ("Add support for
SSH certificate authentication", 2018-06-14) which has been merged in
and tagged as 8.0.0, so GITLAB_SHELL_VERSION needs to be bumped.

Merging this closes gitlab-org/gitlab-ce#34572 see
gitlab-org/gitlab-shell!207 for the gitlab-shell MR.

Implementation notes:

 - The APIs being changed here are all internal, and their sole
   consumer is gitlab-shell.

 - Most of the changed code is a MR to gitlab-shell, see the
   gitlab-org/gitlab-shell!207 MR. That change covers why only some of
   the internal methods get a new "username" parameter, and why some
   others only get a "user_id".

Fixes a NoMethodError in the pre-receive hook: https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/206

This includes the change that prints the @username of a user instead
of the full name.

https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/204

gitlab-shell 5.10.3 does not introduce any new features; it just removes an
unused config option.

Note the dependency on gitlab-shell v5.10.0

Fixes gitaly#629

See gitlab-shell!169

This fixes an issue where the merge request URLs for a push returned an error,
which made gitlab-shell show a stacktrace to the user.

Update to >= 5.1.0 needed for https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2240 on EE.
Updated here to keep CE and EE on the same version.
5.1.1 includes https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/142 to revert changes which were causing problems with Post Receive hooks.

This change continues with the plan to change the parameters passed
around GitLab components to allow for independence of mount points. See
https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/130#note_28747613

This reverts commit 0d55def4.

This change continues with the plan to change the parameters passed
around GitLab components to allow for independence of mount points. See
https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/130#note_28747613

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Related to gitlab-ee#1648

This fixes a compatibility issue with Git 2.11:

- Issue: gitlab-org/gitlab-ce#25301
- gitlab-shell MR: gitlab-org/gitlab-shell!112
- CE MR: gitlab-org/gitlab-ce!7967
- EE MR: gitlab-org/gitlab-ee!964

Signed-off-by: Rémy Coutable <remy@rymai.me>