[META] Split gitlab cookbook into separate cookbooks

The gitlab cookbook should be split into smaller, more specific cookbooks. See !1573 (merged) for an example of how this was done with the registry cookbook.

Keep the following in mind:

• For cookbooks that manage services, there should at least be an enable and a disable recipe
• When splitting out cookbooks, remove ['gitlab'] from the attribute tree. So node['gitlab']['foo'] should become node['foo']
• Use foodcritic on the coobkooks to help catch any potential issues

We should end up with the following cookbooks/recipes moved out:

• Registry
• Gitaly
• GitLab Prometheus
  • gitlab-prometheus.rb
  • node-exporter.rb
  • postgres-exporter.rb
  • prometheus_user.rb
  • redis-exporter.rb
• GitLab Monitor
• GitLab Pages
• Logging
  • logrotate_folders_and_configs.rb
  • Remote Syslog
• Mailroom
• Mattermost
• Nginx
• PostgreSQL
  • postgresql-bin.rb
  • postgresql-user.rb
• Redis
• Sidekiq

Related to #2078