Add #15849 to 4.3.0 release notes

[ci skip]

(cherry picked from commit b8777fc)

Author: michaelklishin

release-notes/4.3.0.md

@@ -200,6 +200,12 @@ compared to other versions.
 
    GitHub issue: [#13885](https://github.com/rabbitmq/rabbitmq-server/pull/13885)
 
+ * The `x-modulus-hash` exchange type, previously provided by the sharding plugin, was moved
+   into the core and reworked to provide stable message routing (distribution)
+   assuming a stable set of bindings, including between node restarts.
+
+   GitHub issue: [#15849](https://github.com/rabbitmq/rabbitmq-server/pull/15849)
+
  * When quorum queue members (replicas) are deleted from a node, either manually
    via `rabbitmq-queues shrink` or as part of `rabbitmqctl forget_cluster_node`,
    the members are stopped in parallel.
@@ -370,6 +376,17 @@ auth_http.authorization_failure_disclosure = true
    GitHub issue: [#14641](https://github.com/rabbitmq/rabbitmq-server/pull/14641)
 
 
+### Sharding Plugin
+
+#### Enhancements
+
+ * The `x-modulus-hash` exchange type, previously provided by the sharding plugin, was moved
+   into the core and reworked to provide stable message routing (distribution)
+   assuming a stable set of bindings, including between node restarts.
+
+   GitHub issue: [#15849](https://github.com/rabbitmq/rabbitmq-server/pull/15849)
+
+
 ### Tracing Plugin
 
 #### Bug Fixes