Feat[MQB]: apply plugin into authentication

[emelialei88]

This PR apply plugin into authentication and reauthentication when we as a broker receives authentication requests from clients.

• Added component rawclient to support integration test test_authn.py.
• Used plugin to authenticate and reauthenticate.
  • Authenticator is managed by TransportManager and referred to by InitialConnectionHandler, since the lifetime of an Authenticator is longer than InitialConnectionHandler.
  • When sending response, we use the same encoding type as the one used by the client AuthenticationRequest.
  • Authentication with plugin is performed in a separate thread, and the channel is closed when there's a failure.
  • When AuthenticationContext is created during initial connection, create a reauthenticateCb to be called when a client session later receives an AuthenticationEvent.
  • Use AuthenticationContext::State to indicate the state of authentication. This is used as a synchronization primitive to make sure only one authentication is run for a given context.
• Basic default authentication credential logic:
  • Use hardcoded credential and basicpass plugin as default way to authenticate if the negotiation message comes first.