Registers a service account with subscriber privileges on the Pub/Sub topic for this Channel Services account or integrator. After you create a subscriber, you get the events through SubscriberEvent Possible error codes: * PERMISSION_DENIED: The reseller account making the request and the provided reseller account are different, or the impersonated user is not a super admin. * INVALID_ARGUMENT: Required request parameters are missing or invalid. * INTERNAL: Any non-user error related to a technical issue in the backend. Contact Cloud Channel support. * UNKNOWN: Any non-user error related to a technical issue in the backend. Contact Cloud Channel support. Return value: The topic name with the registered service email address.