Use structured format for Kafka SampleProducer

[shnplr]

The examples/kafka/src/main/java/io/cloudevents/examples/kafka/SampleProducer.java indicates a structured event but delivers a binary event.

// Configure the CloudEventSerializer to emit events as json structured events
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, CloudEventSerializer.class);
props.put(CloudEventSerializer.ENCODING_CONFIG, Encoding.BINARY);
props.put(CloudEventSerializer.EVENT_FORMAT_CONFIG, JsonFormat.CONTENT_TYPE);

Should this be Encoding.STRUCTURED?

[slinkydeveloper]

Yep this is either a bad comment or bad code, are you willing to provide the fix?