replication.synchro_queue_max_size configuration option added

Fixes #4749

Author: maryiaLichko

doc/reference/configuration/configuration_reference.rst

@@ -4153,7 +4153,7 @@ autoexpel full example
 
     **Since:** :doc:`3.3.0 </release/3.3.0>`
 
-    The maximum size of the synchronous transaction queue on a master node, in bytes.
+    The maximum size of the synchronous transaction queue on a master node, in bytes. The size limit isn't strict, i.e. if there's at least one free byte, the whole write request fits and no blocking is involved.
     This parameter ensures that the queue does not grow indefinitely, potentially impacting performance and resource usage, and applies only to the master node.
 
     The ``0`` value disables the limit.