Add CHANGES and release note for [GL #2732]

CHANGES

@@ -1,3 +1,6 @@
+5651.	[func]		Refactor zone dumping to be processed asynchronously
+			via the uv_work_t thread pool API. [GL #2732]
+
 5650.	[bug]		Prevent a crash that could occur if serve-stale
 			was enabled and a prefetch was triggered during a
 			query restart. [GL #2733]

doc/notes/notes-current.rst

@@ -33,6 +33,9 @@ New Features
   became clogged up with queries that are too old and have already timeouted
   on the receiving side. :gl:`#2313`
 
+- Run zone dumping tasks on separate asynchronous thread pools.  This change
+  makes zone dumping no longer block networking I/O. :gl:`#2732`
+
 Removed Features
 ~~~~~~~~~~~~~~~~