private SchedulerStateChangeListener createJMVersionUpgradeListener() {
    return () -> {
      LOG.info("Job model version upgrade detected.");
      versionUpgradeDetected.getAndSet(true);
      onNewJobModelAvailable(leaderBlob.getJobModelVersion());
    };
  }
Creates a listener for JMVersionUpgradeScheduler class.
Invoked when the processor detects a job model version upgrade on the blob.
Stops listening for job model version upgrades until rebalancing achieved.
@return an instance of SchedulerStateChangeListener.
samza-azure/src/main/java/org/apache/samza/coordinator/AzureJobCoordinator.java