Support warm-up flow control

[caozhiw]

std::shared_ptr<TrafficShapingController> FlowRuleManager::GenerateController(
    const FlowRule& rule) {
  if (rule.metric_type() == FlowMetricType::kQps) {
    switch (rule.control_behavior()) {
      case FlowControlBehavior::kWarmUp:
        // return (WarmUpCalculator, DefaultChecker);
      case FlowControlBehavior::kThrotting:
        // return (DefaultCalculator, ThrottlingChecker);
      default:
        // Default mode or unknown mode: default traffic shaping controller
        return CreateDefaultController(rule);
    }
  }
  return CreateDefaultController(rule);
}

从上面的代码来看，warm up mode 还未实现么？

[sczyh30]

Warm-up has not been supported yet. Contributions are welcomed.