Include Kafka Message Key in Events

[butschi84]

I suggest to include the "message key" (from the events in the kafka message queue) in the event that is being put into the event-driven-ansible queue because it can be very useful when filtering for certain events in an ansible-rulebook.

Therefore this file would have to be changed:
extensions/eda/plugins/event_sources/kafka.py
to something like:

 async for msg in kafka_consumer:
            try:
                data = json.loads(msg.value)
                data["key"] = msg.key.decode('utf-8')
                await queue.put(data)
...

After this change i can listen for events with certain key in the rulebook:

- name: listen kafka
  hosts: all
  sources:
    - ansible.eda.kafka:
        host: 7.7.7.7
        port: 30051
        topic: my-topic
        group_id: ansible-eda
  rules:
    - name: kafka
      condition: event.key == "test-0"
      action:
        run_playbook:
          name: do-something.yml