Fix https alerting

Currently, the HTTPS alerts on staging is unhappy with 7 out of the 8 defined hosts.

This is because

1. The public facing staging site requires authentication (HTTP 401)
2. Payments returns a 404 (file not found) since 72317aba
3. Monitoring has only one of the two domains in its TLS cert.

This MR addresses (1) and (2) by not alerting anymore on those HTTP response codes (will still alert on all other codes including no code - meaning couldn't connect) and address (3) by adding the extra domain into the monitoring server's TLS cert, similar to how issuer is doing it.