refactor: Simplified the configuration for the kafka-services

refactor: Simplified the configuration for the kafka-services

* Removed class `ChannelTaskRunner` and `KafkaServicesApplicationRunner`.
* Instead, the method `ChannelTaskExecutor.excuteChannelTask()` is executed
  as `@Bean.initMethod` by Spring.
* Adapted the test-cases accordingly:
** Joinig the channel-tasks is not necessary any more, because that is
   done by the imported production-config
** `KafkaConfigurationIT` has to call `executeChannelTasks()`
   explicitly
** Therefore, it has to overrule the default-config for the bean
   `dataChannelTaskExecutor` in order to drop the configuration of the
   `initMethod`.
** Otherwise, the test would (might) not restore the data from the topic,
   because the messages, that are send into the test-cluster, might arrive
   only after the initial loading of the data is done.