Allow client authorization on control port ADD_ONION services
We should extend the control port ADD_ONION command from #6411 (moved) to support HS client authorization. This would be useful to Ricochet, and probably other projects.
It's also more important to allow changing an existing service when we might want to add or remove authorized clients, so an UPDATE_ONION command would be useful and probably not difficult.
I'd like to see this done before 0.2.7 is final, so I'm going to look into it.