int getCredits(int opId, Object ... args) {
    return (creditFn == null) ? 1 : creditFn.getCredits(opId, args);
  }
Set up waitTimeMetric metric for latency reporting due to throttling.
@param timer waitTimeMetric metric
samza-api/src/main/java/org/apache/samza/table/remote/TableRateLimiter.java