The availability status requester we've got is not appending the correct account number to the "update the availability status for this endpoint" requests.

1. The handler preloads a source with some of its relations on "source_hanlders.go#SourceCheckAvailability". More specifically, it preloads "source types", "applications", "applications.applicationtypes", "endpoints", "tenant".
2. On the "service/availability_check.go#publishSatelliteMessage" though, the "source.endpoint.tenant" relation is accessed, which hasn't been preloaded.

This causes the header not to have the "r-xh-identity" or "x-rh-sources-account-number" filled with the correct account number.