Update external prometheus config
Update external prometheus config

Updated to include missing metrics:
    * GitLab Workhorse
    * Nginx
    * Sidekiq

mmkassem/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq