Kafka Message Key discarded; Channel ID instead?

[amihalik]

A Kafka Message (or Record) is composed of a Key, Value, and Timestamp and there are currently use cases where data in the Message Key is needed to properly process the Message Value. In these cases, the GeoEvent Adapter will require both the Message Key and Message Value to create a GeoEvent.

The current KafkaInboundTransport drops the Message Key on the floor. I propose that the Message Key is used as the Channel ID. If we pass the Message Key as the Channel ID, the GeoEvent Adapter will have both the Message Key and Value when it deserializes the GeoEvent.