Support handleSerializationError in DlqProductionExceptionHandler for…

[AnkurSinhaaa]

#524

Summary

Overriden handleSerializationError() in DlqProductionExceptionHandler so that serialization exceptions (e.g., poison pill records) can optionally be routed to the DLQ instead of crashing the application.

Changes

• DlqProductionExceptionHandler – Implemented handleSerializationError() with opt-in DLQ routing controlled by a new config flag. Added JavaDoc to all methods.
• KstreamplifyConfig – Added dlq.production-handler.continue-on-serialization-exception property constant.
• DlqProductionExceptionHandlerTest – Added 4 tests covering: flag disabled → FAIL, flag enabled but no DLQ → FAIL, flag enabled with DLQ → RESUME + record in DLQ, internal error during handling → RESUME.
• application.yml / README.md – Documented the new configuration property.

kafka:
  properties:
    dlq:
      production-handler:
        continue-on-serialization-exception: true

[loicgreffier]

@AnkurSinhaaa Looks good for me