doc: tor.md updates (19961)

Summary:

doc: update tor.md address examples from onion v2 to v3

doc: add tor.md section on how to get tor info via bitcoind

doc: update -externalip documentation in tor.md

This is a backport of core#19961

Test Plan: proofreading

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11031