spring-projectsGH-2800: provide doc for the custom DLT routing feature

Fixes spring-projects#2800

spring-kafka-docs/src/main/antora/modules/ROOT/pages/retrytopic/features.adoc

@@ -261,3 +261,41 @@ protected Consumer<DeadLetterPublishingRecovererFactory>
 
 It is recommended that you use the provided resolvers when constructing the custom instance.
 
+[[exc-based-custom-dlt-routing]]
+== Routing of messages to custom DLTs based on thrown exceptions
+
+Starting with version 3.2.0, it's possible to route messages to custom DLTs based on the type of the exception, which has been thrown during their processing.
+In order to do that, you need to specify the routing.
+Routing customization consists of the specification of the additional destinations.
+Destinations in turn consist of two settings: the `suffix` and `exceptions`.
+When the exception type specified in `exceptions` has been thrown, the DLT containing the `suffix` will be considered as the target topic for the message before the general purpose DLT is considered.
+Take a look at the examples:
+
+[source, java]
+----
+@RetryableTopic(exceptionBasedDltRouting = {
+    @ExceptionBasedDltDestination(
+        suffix = "-deserialization", exceptions = {DeserializationException.class}
+    )}
+)
+@KafkaListener(topics = "my-annotated-topic")
+public void processMessage(MyPojo message) {
+    // ... message processing
+}
+----
+
+[source, java]
+----
+@Bean
+public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
+    return RetryTopicConfigurationBuilder
+            .newInstance()
+            .dltRoutingRules(Map.of("-deserialization", Set.of(DeserializationException.class)))
+            .create(kafkaOperations)
+            .create(template);
+}
+----
+
+`suffix` takes place before the general `dltTopicSuffix` in the custom DLT name.
+Considering presented examples, the message, which caused the `DeserializationException` will be routed to the `my-annotated-topic-deserialization-dlt` instead of the `my-annotated-topic-dlt`.
+Custom DLTs will be created following the same rules as stated in the xref:retrytopic/features.adoc#topics-autocreation[Topics AutoCreation].