Add the prometheus_monitoring config entry

This is so we can disable prometheus

metadata.rb

@@ -4,7 +4,7 @@ maintainer_email 'marin@gitlab.com'
 license          'All rights reserved'
 description      'Installs/Configures GitLab using omnibus-gitlab'
 long_description 'Installs/Configures GitLab using omnibus-gitlab'
-version          '0.3.15'
+version          '0.3.16'
 issues_url       'https://gitlab.com/gitlab-org/cookbook-omnibus-gitlab/issues'
 source_url       'https://gitlab.com/gitlab-org/cookbook-omnibus-gitlab/'

templates/default/gitlab.rb.erb

@@ -51,6 +51,7 @@ node_exporter
 redis_exporter
 postgres_exporter
 gitlab_monitor
+prometheus_monitoring
   }.each do |svc| %>
 <%   if @gitlab_rb[svc] %>