Updates gitlab to the current stable version and fixes a lot of features that
were broken, at least with the current version and our configuration.
Quite a lot of sweat and tears has gone into testing nearly all features and
reading/patching the Gitlab source as we're about to deploy gitlab for our
whole company.
Things to note:
* The gitlab config is now written as a nix attribute set and will be
converted to JSON. Gitlab uses YAML but JSON is a subset of YAML.
The `extraConfig` opition is also an attribute set that will be merged
with the default config. This way *all* Gitlab options are supported.
* Some paths like uploads and configs are hardcoded in rails (at least
after my study of the Gitlab source). This is why they are linked from
the Gitlab root to /run/gitlab and then linked to the configurable
`statePath`.
* Backup & restore should work out of the box from another Gitlab instance.
* gitlab-git-http-server has been replaced by gitlab-workhorse upstream.
Push & pull over HTTPS works perfectly. Communication to gitlab is done
over unix sockets. An HTTP server is required to proxy requests to
gitlab-workhorse over another unix socket at
`/run/gitlab/gitlab-workhorse.socket`.
* The user & group running gitlab are now configurable. These can even be
changed for live instances.
* The initial email address & password of the root user can be configured.
Fixes #8598.
