spring-kafka-test is missing from spring-boot-starter-kafka-test

[mhalbritter]

[armandjudicael]

i'd like to contribute for this one

[snicoll]

@armandjudicael thanks for the offer, and sorry I had missed your comment. I've started to work on this and it isn't a straightforward change as spring-kafka-test requires some additional checks.

[snicoll]

When this is done, we should make sure to remove the superflous dependency in the Kafka smoke test.