Add additional_labels parameter (#1160)

* Move label templates into `common` role

So that there is single source of labels management, and labels are
unified across the other roles

* Introduce `additional_labels`
* Fix paths for labels templates
* Return `additional_labels_items` as list
* Add molecule tests

roles/backup/defaults/main.yml

@@ -31,6 +31,9 @@ backup_resource_requirements:
 # Allow additional parameters to be added to the pg_dump backup command
 pg_dump_suffix: ''
 
+# Labels defined on the resource, which should be propagated to child resources
+additional_labels: []
+
 # Maintain some of the recommended `app.kubernetes.io/*` labels on the resource (self)
 set_self_labels: true
 ...