Adding config option for worker poll duration to avoid consumer join issues (#14818)

[rainerschamm]

Added a new config option:

  private static final String WORKER_POLL_DURATION_MS_PROP = "iceberg.worker.poll.duration-ms";
  private static final int WORKER_POLL_DURATION_MS_DEFAULT = 0;

I kept the duration at 0 so that there in effect no change to the existing behavior in Worker.java:

   void process() {
-    consumeAvailable(Duration.ZERO);
+    consumeAvailable(pollDuration);
   }