GH-2448: State Non-Blocking Retries API Status

Resolves #2448

Author: garyrussell

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

@@ -1,14 +1,8 @@
 [[retry-topic]]
 === Non-Blocking Retries
 
-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.
-
 Version 2.9 changed the mechanism to bootstrap infrastructure beans; see <<retry-config>> for the two mechanisms that are now required to bootstrap the feature.
 
-After these changes, we are intending to remove the experimental designation, probably in version 3.0.
-
 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

@@ -32,6 +32,8 @@ See <<same-broker-multiple-tests>> for more information.
 [[x30-retryable]]
 ==== Retryable Topics Changes
 
+This feature is no longer considered experimental (as far as its API is concerned), the feature itself has been supported since 2.7, but with a greater than normal possibility of breaking API changes.
+
 The bootstrapping of <<retry-topic>> infrastructure beans has changed in this release to avoid some timing problems that occurred in some application regarding application initialization.
 See <<retry-config>> for more information.