Add an endpoint to accept deal letter message from active consumer

[stevehu]

For ReactiveConsumer, we return a list of processed messages to the Kafka-sidecar and partial of the messages with failure status should be put into the dead letter queue/topic.

For ActiveConsumer, the backend should actively access the sidecar API to insert messages to the dead letter queue. During the backend processing, once a message is not processed successfully, we should invoke the sidecar API to insert the message to the dead letter queue.

The format of the dead letter message should be the same as the ReactiveConsumer.