- Purge the workhorse helper methods that had been refactored out from
  other files and clean up the affected spec tests to pass

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

- Remove the workhorse helper methods that are refactored out
- Fix workhorse helper tests

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

- Adds a suite of rspec tests for the gitlab workhorse helper
- Checks for and removes orphan workhorse socket files if present

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

- Changes the socket_file_path to be the listen_address method in the
  Workhorse helper per review discussion

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

- Run the SELinux helper after GitLab Workhorse and other files are
  created ensuring their file contexts are restored
- Place GitLab Workhorse socket files into a sockets directory allowing
  the SELinux file context to be inherited on service restarts
- Add a GitLab Workhorse helper to ensure that new UNIX sockets for
  Workhorse always inherit the proper SELinux file context

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

This also moves the worker pool size setting to an ENV variable
since that was changed in gitlab-rails

As discussed in
https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/4324, we
can set the default attribute for `gitlab_workhorse['auth_socket']` to
`nil` as the empty string value so we can use
`node['gitlab']['gitlab-workhorse']['auth_socket']` in the template
instead of `Gitlab['gitlab_workhorse']['auth_socket']`.

In Workhorse, it's not absolutely necessary to have both -authSocket and
-authBackend arguments, as long as least one is available to all GitLab
application hosts. In a single-node Ominbus install, -authSocket will
suffice, but in multi-node installations -authBackend may only be
needed.

To support the second case and make it possible to disable listening to
a UNIX socket, admins can do the following:

```
gitlab_workhorse['auth_socket'] = nil
gitlab_workhorse['auth_backend'] = 'https://workhorse.example.com'
```

* Enable workhorse metrics on `localhost:9229` by default.
* Add to Prometheus scrape config.

Closes https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1595