code: public PerformanceMetrics createNext(String nextAction, String nextDescriptor) {
      return createNext(nextAction, nextDescriptor, null);
    }
docs: Creates new instance of performance metrics. Stores the key and correlation id of the parent metrics instance.
  Assigns next level.
  @param nextAction a short name of measured operation, typically a first prefix of descriptor
  @param nextDescriptor a full description of measured operation
  @return PerformanceMetrics a new instance of performance metrics with stored key and correlationId from the parent
  metrics and assigned next level