Serialise service, API keys and permissions

By serialising these straight away we can:
- not go back to the database later, potentially closing the connection
  sooner
- potentially cache the serialised data, meaning we don’t touch the
  database at all

app/notifications/process_notifications.py

@@ -123,7 +123,6 @@ def persist_notification(
         template_version=template_version,
         to=recipient,
         service_id=service.id,
-        service=service,
         personalisation=personalisation,
         notification_type=notification_type,
         api_key_id=api_key_id,