[net/refactor] Add AddrFetch connections to ConnectionType enum

Summary:

- AddrFetch connections are short lived connections used to getaddr from
a peer
- previously called "one shot" connections

Partial backport (7/19) of core PR19316:
https://github.com/bitcoin/bitcoin/pull/19316/commits/442abae2bac7bff85886143df01e14215532b974

Depends on D8716.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8717