doc: add detached release notes for #14060

doc/release-notes-14060.md

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+Configuration
+-------------
+
+The outbound message high water mark of the ZMQ PUB sockets are now
+configurable via the options:
+
+`-zmqpubhashtxhwm=n`
+
+`-zmqpubhashblockhwm=n`
+
+`-zmqpubrawblockhwm=n`
+
+`-zmqpubrawtxhwm=n`
+
+Each high water mark value must be an integer greater than or equal to 0.
+The high water mark limits the maximum number of messages that ZMQ will
+queue in memory for any single subscriber. A value of 0 means no limit.
+When not specified, the default value continues to be 1000.
+When a ZMQ PUB socket reaches its high water mark for a subscriber, then
+additional messages to the subscriber are dropped until the number of
+queued messages again falls below the high water mark value.