[bitcoin/bitcoin] configurable ZMQ message limit (#13315)

thanks for the reply, @jmcorgan
First of all, it is a volunteer project for me as well. Tbh, I’m not even that interested in this change, but
the LND folks have been complaining about it for over a year, and it seems important, so I investigated the issue, made a case and provided evidence.
(Why? because I worked with ZMQ before, so I knew about this issue for some years already. And I like to fix stuff.)

My task is to identify problems (not a popular thing to do, but someone has to do it).
What I’ve done is identifying a issue that was a big question-mark for some for years and provided evidence. I’ve mentioned the issue a few times on different platforms, but it seems these kind of things do not communicate well in a chat. As a result, I wrote it down in a ticket, with proof, and some code.

I created some code only to make a case — I don’t claim any proficiency in C++ so I want others to improve it. It should be low-hanging fruit for everyone else.

Over the last months I’ve patiently waited and tried to contact you a few times (as have others) but never got a response. (that is just rude)
I’ve created the code to make it configurable, as suggested by some — even though we all know that is pointless without figuring out FIRST what a functional HWM value should be anyway; it doesn’t even solve the issue, and no one who suggested it made a case for why it would solve anything…

I’ve asked you (or anyone else) to suggest a better a default HWM value; never got a reply. The reason why seems quite obvious: no one actually tested what the right value is on their system.
The current ‘1000’ is a arbitrary value, which doesn’t make any sense when you think about it.

(as a scientist) I ask you to defend why ‘1000’ is the correct value