Add the admin_update_sql module

This allows to upgrade from the old database schema to the new one that
works for multiple virtual hosts:
https://blog.process-one.net/ejabberd-18-03/

    ejabberdctl update_sql

site-cookbooks/kosmos-ejabberd/templates/ejabberd.yml.erb

@@ -161,6 +161,7 @@ acme:
 modules:
   mod_adhoc: {}
   mod_admin_extra: {}
+  mod_admin_update_sql: {}
   mod_announce:
     access: announce
   mod_avatar: {}