Point to rabbit and kafka confi samples. Explain how to use with third party binders.

[ericis]

All Spring Cloud Bus examples refer to RabbitMQ and Kafka, but only provide RabbitMQ configuration examples.

Please add kafka configuration to documentation.

[spencergibb]

I see one example of rabbitmq configuration. I think, in fact, we shouldn't show any and we should link to the proper places to find configuration for rabbit and kafka. Bus will also work with other spring cloud stream binders. We would end up with an explosion of examples.