Move cornichon-kafka in a dedicated repo.

[agourlay]

The test for the Kafka DSL is really flaky which makes the whole projects build red.

I tried to understand the root issue but made not progress so far.

Starting scenario 'write and read arbitrary Strings to/from topic'

Starting scenario 'use cornichon jsonAssertions on the message value'

- **failed** write and read arbitrary Strings to/from topic [2634 ms]

  Scenario 'write and read arbitrary Strings to/from topic' failed:

  

  at step:

  When I reading the last 1 messages from topic=cornichon

  

  with error(s):

  Not enough messages polled, expected at least 1 but got 0

  

  

  seed for the run was '1576850996627'

  replay only this scenario with the command:

  testOnly *KafkaExample -- "write and read arbitrary Strings to/from topic" "--seed=1576850996627"

   Scenario : write and read arbitrary Strings to/from topic

      main steps

      Given I put message=I am a plain string with key=success to topic=cornichon [206 ms]

      When I reading the last 1 messages from topic=cornichon [798 ms]

      *** FAILED ***

      Not enough messages polled, expected at least 1 but got 0

[agourlay]

I have been able to stabilize the tests, it is not an issue anymore.