Make rpID required when generating authentication options

[MasterKale]

Describe the issue

I'm going to make the rpID argument required when calling generateAuthenticationOptions(), for consistency with generateRegistrationOptions(). There's no point in letting it be optional during auth when one has already been chosen for registration. RP ID scoping is also easy to mess up, so let's encourage devs to move towards the safer solution of explicitly defining an RP ID for both ceremonies.

[MasterKale]

This change is now available in the recently-published @simplewebauthn/server@10.0.0 ✌️