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']`.