doc: Add release notes for 15596

Summary:
This is a partial backport of Core PR15596 : https://github.com/bitcoin/bitcoin/pull/15596/commits/fabfb79673d6bf9bff5258cd709d8294e77c1764

Depends on D6223

Test Plan: Read.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D6224