MethodLevelListener does not handle different payloads for same topic/queue

[timonback]

Describe the bug
While the AbstractOperationDataScanner can handle multiple payloads for one topic/queue, the AbstractMethodLevelListenerScanner uses only the first payload and ignores the others.

When multiple payloads (via ChannelItem) are found for one topic, the payloads should be merged together using anyOf. This is implemented in MessageHelper.

Reported in #64

Dependencies and versions used

• springwolf-amqp version 0.16.0.
• springwolf-kafka version 0.16.0.

Code example

public class ExampleConsumer {

    private final ExampleProducer exampleProducer;

    @RabbitListener(queues = "example-queue") // same queue
    public void receiveExamplePayload(ExamplePayloadDto payload) {
        log.info("Received new message in example-queue: {}", payload.toString());
        exampleProducer.sendMessage(payload);
    }

    @RabbitListener(queues = "example-queue") // same queue
    public void receiveAnotherPayload(AnotherPayloadDto payload) {
        log.info("Received new message in another-queue: {}", payload.toString());
    }
}

Stack trace and error logs
none