Support warm-up flow control

```c++
std::shared_ptr 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？

Start at FlowRuleManager::GenerateController and inspect the referenced WarmUpCalculator, DefaultCalculator, DefaultChecker, and ThrottlingChecker types to understand the intended flow-control behavior. Confirm whether the warm-up branch is implemented elsewhere and define completion as warm-up rules selecting the appropriate controller rather than falling back to the default path.

Written by the indexing model from the issue text.