Review the kafka-clients and vertx-kafka-client module

During the works on EAP7-1405 and EAP7-1659, there is mentioned that some classes from Apache Kafka Client jar (org.apache.kafka:kafka-clients) are exposed to be used by user, e.g. here in this WildFly proposal for EAP7-1659.

AFAIK there is no kafka-clients module that could expose particular classes. There has been added just a `vertx-kafka-client` module into the WildFly server, see this module.xml. Which is private and I believe it is correct.

TBH - I don't see any warning when utilizing mentioned classes from Apache Kafka Clients jar, which is confusing to me. My expectation is that we should see warning when these classes are used in a user deployment and to avoid this, we shall introduce an appropriate module which exposes particular packages only.

Apart from this, it would be very nice to have these necessary exposed classes rather in some API module instead of using the Apache Kafka Clients, although based on this documentation, it looks that it's supposed to be used this way.