Add Zuul to backups group

With I37dcce3a67477ad3b2c36f2fd3657af18bc25c40 we removed the
configuration managment of backups on the zuul server, which was
happening via puppet.  So the server continues in it's last state, but
if we ever built a fresh server it would not have backups.

Add it into the Ansible backup group, and uncomment the backup-server
group to get a run and setup the Ansible-managed backups.

Change-Id: I0af6b7fedc2f8f5a7f214771918138f72d298325

inventory/service/groups.yaml

@@ -25,8 +25,9 @@ groups:
     - gitea01.opendev.org
     - review[0-9]*.openstack.org
     - review-dev[0-9]*.open*.org
-#  backup-server:
-#    - backup[0-9]*.opendev.org
+    - zuul[0-9]*.opendev.org
+  backup-server:
+    - backup[0-9]*.opendev.org
   cacti: cacti[0-9]*.open*.org
   certcheck:
     - cacti[0-9]*.open*.org