mqtt-kafka binding uses 2 different consumer groups per mqtt client

[jfallows]

Describe the bug
mqtt-kafka binding uses 2 different consumer groups per mqtt client (instead of just one).

To Reproduce
Steps to reproduce the behavior:

1. Run mqtt.kafka.broker example
2. Connect mqtt client
3. List consumer groups in Kafka
4. See multiple consumer groups created for the same mqtt client

Expected behavior
There should be only one consumer group for each mqtt client.

Screenshots
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Additional context
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