Postgres doesn't allow connections via hostname

This role needs to delegate the database tasks to a database host -
which sometimes is the same host that runs Zammad
(delegate_to: localhost doesn't work because it wants to run the
tasks at the Ansible controler)
We need to distinguish between the database_host and the zammad_database_host
The later one can be set to 127.0.0.1 to allow local database connections
without using the hostname

templates/database.yml.j2

@@ -5,7 +5,7 @@ default: &default
   adapter: postgresql
   username: {{ zammad_database_user }}
   password: {{ zammad_database_password }}
-  host: {{ database_host }}
+  host: {{ zammad_database_host }}
 
 production:
   <<: *default