Justify the choice of ADDR cache lifetime

Summary:
PR description

This is a follow-up on #18991 which does 3 things:

• improves privacy of a node listening to multiple addresses via adding cache index by local socket addr (suggested here)
  • documents on the choice of 24h cache lifetime
• addresses nits from "Cache responses to GETADDR to prevent topology leaks" #18991

This is a backport of core#19697 [1/4]
https://github.com/bitcoin/bitcoin/pull/19697/commits/42ec5585424ceb91bed07826dde15697c020661a

Test Plan: ninja

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10290