Improve onion key and TLS management

As a best practice behavior, a relay should check that the onion key it tried to publish is actually the one it sees in the consensus in which it appears.

The onion key should also be what authenticates the TLS key (rather than the identity key, as it is now).

This would prevent some utility vectors of identity key theft, where a non-targeted upstream MITM attempts to use a relays identity to impersonate it in order to execute a tagging attack (#5456 (moved)).