gitlab: enable custom pages root dir

As per docs: https://docs.gitlab.com/ee/user/project/pages/introduction.html#customize-the-default-folder

roles/gitlab/tasks/main.yml

@@ -43,7 +43,7 @@
         gitlab_pages['external_https'] = {{ gitlab_pages_https_addresses }}
         gitlab_pages['rate_limit_source_ip'] = 10.0
         gitlab_pages['rate_limit_source_ip_burst'] = 300
-        gitlab_pages['env'] = {'FF_ENFORCE_IP_RATE_LIMITS' => 'true'}
+        gitlab_pages['env'] = { 'FF_ENFORCE_IP_RATE_LIMITS' => 'true', 'FF_CONFIGURABLE_ROOT_DIR' => 'true' }
         letsencrypt['enable'] = true
         letsencrypt['contact_emails'] = ['webmaster@archlinux.org']
         gitlab_rails['env'] = {'GITLAB_THROTTLE_BYPASS_HEADER' => 'Gitlab-Bypass-Rate-Limiting'}