Add "What's New" For Retry Topics

Author: garyrussell

spring-kafka-docs/src/main/asciidoc/retrytopic.adoc

@@ -3,6 +3,7 @@
 
 IMPORTANT: This is an experimental feature and the usual rule of no breaking API changes does not apply to this feature until the experimental designation is removed.
 Users are encouraged to try out the feature and provide feedback via GitHub Issues or GitHub discussions.
+This is regarding the API only; the feature is considered to be complete, and robust.
 
 Achieving non-blocking retry / dlt functionality with Kafka usually requires setting up extra topics and creating and configuring the corresponding listeners.
 Since 2.7 Spring for Apache Kafka offers support for that via the `@RetryableTopic` annotation and `RetryTopicConfiguration` class to simplify that bootstrapping.

spring-kafka-docs/src/main/asciidoc/whats-new.adoc

@@ -8,6 +8,14 @@ For changes in earlier version, see <<history>>.
 
 This version requires the 2.7.0 `kafka-clients`.
 
+[[x-27-nonblock-retry]]
+==== Non-Blocking Delayed Retries Using Topics
+
+This significant new feature is added in this release.
+When strict ordering is not important, failed deliveries can be sent to another topic to be consumed later.
+A series of such retry topics can be configured, with increasing delays.
+See <<retry-topic>> for more information.
+
 [[x27-container]]
 ==== Listener Container Changes