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 closesgitlab-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".
