Major Description
Currently producerIds are maintained in Zookeeper but in the future we'd like them to be managed by the controller quorum in an internal topic.
The reason for storing this in Zookeeper was that this must be unique across the cluster. In this task it should be refactored such that the TransactionManager turns to the Controller for a ProducerId which connects to Zookeeper to acquire this ID. Since ZK is the single source of truth and the PID won't be cached anywhere it should be safe (just one extra hop added).