Controller support for creating authenticated onion services

As discussed on tor-dev@ the only way to create a v3 onion service with authentication is by writing files to disk within a 'authorized_clients' directory.

Our ADD_ONION command can create authenticated v2 services via its 'BasicAuth' flag, and we can authenticate to a v3 service with ONION_CLIENT_AUTH_ADD. However, there isn't yet a controller mechanism to create a v3 service with authentication. This is intended to track that.