GitLab

    - relative URL support: comment out - we do not need it - gitlab is
      always located at /.

    - Nginx-http: restore our version for proxy_set_header - upstream
      turned to allowing users to configure this, see e.g.

        https://gitlab.com/gitlab-org/omnibus-gitlab/commit/e13d5e42
        https://gitlab.com/gitlab-org/omnibus-gitlab/commit/a450585e

      but doing this way creates more complexity for gitlab SR, so I've
      restored our version which essentially does the same as default in
      omnibus-gitlab, and if we'll need to tune it - we can do directly in
      Nginx config.

      In other words slapos version does not allow users to tune nginx
      headers as instance parameter.