move service to broadcast org when broadcasting is enabled

we want to keep track of all broadcast services across govt easily. As
such, when broadcasting is enabled for a service, we've decided we're
going to add the service to a special broadcasting organisation.

This organisation is defined in the config file. It's hard coded for
production, if you want to test locally, you should set
BROADCAST_ORGANISATION_ID in your local environment.

app/models/service.py

@@ -100,9 +100,16 @@ class Service(JSONModel):
         )
 
     def force_broadcast_permission_on(self):
-        return self.update_permissions(
+        ret = self.update_permissions(
             set(self.permissions) - {'email', 'sms', 'letter'} | {'broadcast'}
         )
+        broadcast_org_id = current_app.config['BROADCAST_ORGANISATION_ID']
+        if broadcast_org_id:
+            organisations_client.update_service_organisation(
+                service_id=self.id,
+                org_id=broadcast_org_id
+            )
+        return ret
 
     def update_permissions(self, permissions):
         return self.update(permissions=list(permissions))