nip-42: successful AUTH must be acknowledged with OK

[Sjors]

In noStrudel I can see in the web socket log that it sends out an AUTH message. In the relay log I see client is authenticated. But there's no OK message.

NIP-42 says:

AUTH messages sent by clients MUST be answered with an OK message, like any EVENT message.

A practical consequence is that noStrudel shows an endless spinner:

[kumulynja]

@thesimplekid nip47 aren't accepted/denied with an OK message either, so I guess this issue might be for all ephemeral event types and can be solved generally for all ephemeral events.