Enable gitlab pages

Fixes #228 (closed) and supersedes !163 (closed). Enables easy resolving of #61 (closed).

The test page is online at https://test.archlinux.org/. Its project is here: https://gitlab.archlinux.org/svenstaro/pages-test/pages It uses the GitLab built-in Let's Encrypt integration.

Changes are already rolled out.

Upon inspection and merging, the reviewer must:

• Remove hetznerdns_record.gitlab_pages_test_* from archlinux.tf and run terraform apply
• Remove the project https://gitlab.archlinux.org/svenstaro/pages-test

roles/archweb/templates/maintenance-nginx.d.conf.j2

@@ -158,7 +158,7 @@ server {
             access_log   /var/log/nginx/{{ archweb_domain }}/access.log main;
             uwsgi_pass archweb;
         }
-            
+
         return 503;
     }