CAMEL-7864: Updates to allow setting Kafka's zookeeper.connect directly.

- Added new property to KafkaConfiguration for zookeeperConnection and
  configured it to override the zookeeperHost and zookeeperPort
  properties.
- Created getZookeeperConnect method on KafkaConfiguration to return
  the zookeeperConnect property if set or the combination of host ":"
  port if zookeeperConnect is not set.
- Added zookeeperConnect get and set methods on KafkaEndpoint to
  delegate to KafkaConfiguration.
- Updated KafkaConsumer to use the getZookeeperConnect method on the
  KafkaEndpoint.
- Added tests for the changes.