code: private Optional<DurationThresholdTracker> requestDurationThresholdTracker(MetricId id,
                                                                               String endpoint) {
      return durationThresholdConfig.getDurationThresholdForEndpoint(endpoint)
          .map(threshold -> Optional.of(new DurationThresholdTracker(id, metricRegistry, threshold)))
          .orElse(Optional.empty());
    }
docs: Checks for endpoint-duration-goal configuration options and sets up
  metrics that track how many requests meet a certain duration threshold goal.
  
  @param endpoint formatted as METHOD:URI