[doc] Describe different connection types

Summary:
Partial backport (8/19) of core PR19316:
https://github.com/bitcoin/bitcoin/pull/19316/commits/46578c03e92a55925308363ccdad04dcfc820d96

Depends on D8717.

Test Plan:

ninja

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8718