Collect aggregate stats of ntor-using hidden service interactions vs tap-using interactions

In legacy/trac#13195 (moved) I have a patch to better understand the fraction of Tor traffic that has to do with hidden services, vs the fraction that has to do with exiting.

For the hidden service traffic, we can see if the handshake that extended that hop of the circuit was done using ntor or with tap.

By remembering this bit, we can track fraction of hidden service traffic that came from old Tor 0.2.3.x style bots, vs newer clients. It would be very useful to see this fraction over time.