Add support for MapAddress
Many onion service users like to define local aliases, like "my-favorite.onion" instead of "big-long-public-key-name.onion". C Tor gives a way to configure this, by defining one address (or one address suffix) to be an alias for another.
We should build something similar in arti; @dgoulet says people use this with onion services.
There is also, in C tor:
- a facility to add and remove mappings from the control port
- An "automap" facility so that when somebody resolves (say) "xyzxyz.onion" from the control port, Tor picks a random unused reserved IPv6 address to associate with that .onion address, and ensures that future requests to that address will be sent to xyzxyz.onion.
These last two features may or may not be necessary.