Add service broadcast settings to `sample_broadcast_service`
Add service broadcast settings to `sample_broadcast_service`

This will make our `sample_broadcast_service` look more realistic.

The one downside to this, is that there will be a short amount of time
where we have broadcast services that do not have a row in the
service_broadcast_settings table until we have backfilled this data. Our
unit tests therefore won't have coverage for this case but I think the
risk is small and acceptable for the moment as this will no longer be
the case in say a weeks time.

alphagov/notifications-api,alphagov/notifications-api