Resolve "gitlab-shell 8.1.1 not on master"

Closes #148 and #145

See merge request gitlab-org/gitlab-shell!230

Revert refactor

Closes #147

See merge request gitlab-org/gitlab-shell!228

This reverts commit 764f6f47.

This reverts commit 3aaf4751, reversing
changes made to c6577e0d.

This reverts commit f4ce4a3c.

Fix two regressions in SSH certificate support (8.1)

See merge request gitlab-org/gitlab-shell!226

Add missing require statement in create-hooks

Closes gitlab-ce#50160

See merge request gitlab-org/gitlab-shell!225

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50160

Pass custom git_config_options to Gitaly

See merge request gitlab-org/gitlab-shell!221

Fix two regressions in my 2e8b6702 ("Add support for SSH certificate
authentication", 2018-06-14) merged in gitlab-org/gitlab-shell!207.

This fixes the issue noted in gitlab-org/gitlab-shell#145 where the
command-line contains things other than the key/user/username, and
also a regression where SSH certificates are being used, and the
username presented in the key is unknown to GitLab.

In that case, we should log the user in as "Anonymous" (on an instance
that allows public access), but because of how the error checking
around api.discover() was implemented we ended up erroring out
instead.

Refactor that focuses on SRP improvements

See merge request gitlab-org/gitlab-shell!214

The /api/internal/allowed endpoint on GitLab has been updated to return some
custom git options that can be used with git commands, we need to pass these received options to Gitaly.

Release v8.1.0

See merge request gitlab-org/gitlab-shell!219

Add Git protocol v2

See merge request gitlab-org/gitlab-shell!217

* Use gl_id when we don't know if it's a key-X or user-X
* Use Actor.new_from(gl_id) which will figure out if it's a Key or User
* Use key_str when we're referring to key-X as key_id is confusing