Add message producer route to kafka example

Currently we start a consumer route and then create messages like this

```
kubectl -n kafka run kafka-producer -ti --image=quay.io/strimzi/kafka:0.30.0-kafka-3.2.0 --rm --restart=Never -- bin/kafka-console-producer.sh --bootstrap-server my-cluster-kafka-bootstrap:9092 --topic my-topic
```

Ideally we'd like to create these messages with camel-k