[bitcoin/bitcoin] ZMQ: add options to configure outbound message high water mark, aka SNDHWM (#14060)

ZMQ: add options to configure outbound message high water mark, aka SNDHWM

This is my attempt at https://github.com/bitcoin/bitcoin/pull/13315
You can view, comment on, or merge this pull request online at:

https://github.com/bitcoin/bitcoin/pull/14060

— Commit Summary —

* ZMQ: add options to configure outbound message high water mark, aka SNDHWM

— File Changes —

M contrib/zmq/zmq_sub.py (1)
M contrib/zmq/zmq_sub3.4.py (1)
M doc/zmq.md (14)
M src/init.cpp (8)
M src/zmq/zmqabstractnotifier.h (3)
M src/zmq/zmqnotificationinterface.cpp (2)
M src/zmq/zmqnotificationinterface.h (2)
M src/zmq/zmqpublishnotifier.cpp (13)

— Patch Links —

https://github.com/bitcoin/bitcoin/pull/14060.patch
https://github.com/bitcoin/bitcoin/pull/14060.diff