distinguish PT vs proxy for real in bootstrap tracker

The bootstrap tracker work in #27167 (moved) adds distinctions (in the form of additional bootstrap phases) between connecting directly to a relay vs connecting through a proxy. It also tries to distinguish proxies from PTs.

The changes to do the distinguishing between PT vs proxy don't work, because conn->proxy_type gets set to the protocol type of the underlying protocol that tor uses to talk to the PT locally.