feat protocol: added authentication transportation hybrid

extended AuthenticatorTransport type with new hybrid value incl. description from official documentation

Fixes go-webauthn#74

protocol/authenticator.go

@@ -99,6 +99,8 @@ const (
  BLE AuthenticatorTransport = "ble"
  // Internal the client should use an internal source like a TPM or SE
  Internal AuthenticatorTransport = "internal"
+ // HYBRID indicates the respective authenticator can be contacted using a combination of (often separate) data-transport and proximity mechanisms. This supports, for example, authentication on a desktop computer using a smartphone.
+ HYBRID AuthenticatorTransport = "hybrid"
 )
 
 // A WebAuthn Relying Party may require user verification for some of its operations but not for others,