feat: allow multiple origins set per RelyingParty

As described in the issue https://github.com/cedarcode/webauthn-ruby/issues/428 when building a Relying Party that is supposed to be used by iOS and Android native clients, we need to be able to specify multiple allowed origins per RP (https://developer.android.com/identity/sign-in/credential-manager#verify-origin) This is yet not supported by this library though is also part of standard specification https://w3c.github.io/webauthn/#sctn-validating-origin

Current workaround is to fallback to creating multiple RP abstractions per expected client platform (Android, iOS, etc) and select one of them based on User-Agent header (for example). That is of course troublesome and can actually be avoided.

This PR allows a relying party to specify either string for origin or array of strings like in the example:

# config/initializers/webauthn.rb

WebAuthn.configure do |config|
  # This value needs to match `window.location.origin` evaluated by
  # the User Agent during registration and authentication ceremonies.
  # config.origin = "https://auth.example.com/"
  config.origin = [
    "https://auth.example.com/",
    "android:apk-key-hash:blablablablablalblalla"
  ]

  # Relying Party name for display purposes
  config.rp_name = "Example Inc."
  config.rp_id  = "example.com"
end

The only drawback of this approach is that in case an array is used for config.origin, - it's impossssible to "guess" relying party by origin (which maybe we should not even do?) thus having array there and no explicitly set config.rp_id would result in RpIdVerificationError which imo should be expected.

Hope this PR makes sense. Please let me know should there be any change requests/questions

cedarcode / webauthn-ruby

feat: allow multiple origins set per RelyingParty #431