Fix code example in the documentation for for Non-Blocking Retries - DLT Failure Behavior

[jucosorin]

Spring Kafka 3.0.0

In the documentation for Non-Blocking Retries on DLT Failure Behaviour there is a code sample that, among other things, shows how to select a DTL handler method. The sample uses the method .dltProcessor(Class<?> clazz, String methodName). This method doesn't exist anymore and one should use .dltHandlerMethod(String beanName, String methodName).

Link to the above mentioned documentation paragraph:

https://docs.spring.io/spring-kafka/docs/current/reference/html/#dlt-failure-behavior