* This could enable specified parameter flow control for customized objects.

* Clear useless data in ParameterMetric for all removed rules

- use AtomicLong to replace AtomicInteger

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Add a ParameterMetricStorage specific for caching ParameterMetric (moved from ParamSlot)
- Add rule map building helper method in ParamFlowRuleUtil so that we can reuse it in other rule managers

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

* support burst count, statistic interval per rule and throttling mode.
* Add fields in ParamFlowRule to support burst count, throttle, statistic interval per rule.
* Deprecate HotParamLeapArray and use token bucket algorithm directly.

- Also rearrangement of some code

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Signed-off-by: Carpenter Lee <hooleeucas@163.com>

* Allow negative paramIndex in ParamFlowRule

Signed-off-by: Carpenter Lee <hooleeucas@163.com>

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- The constructor now accept `sampleCount` and `windowIntervalMs` so that it can match the two basic properties

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Update ParamFlowRule to support cluster mode
- Add `ParamFlowClusterConfig` to provide cluster mode items for the rule
- Update ParamFlowChecker to support cluster flow mode
- Extract ParamFlowRuleUtil class
- Change type of `flowId` from Integer to Long

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Update ParamFlowRule to support cluster mode
- Add `ParamFlowClusterConfig` to provide cluster mode items for the rule
- Update ParamFlowChecker to support cluster flow mode
- Extract ParamFlowRuleUtil class
- Change type of `flowId` from Integer to Long

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Refactor the slot interface to support prioritized entry
- Add `entryWithPriority` in SphU

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

- Add callback registry for statistic slot for extensions.
- Add a new module `sentinel-parameter-flow-control` under `sentinel-extension`.
- Add a `CacheMap` interface to provide abstraction for cache. We use ConcurrentLinkedHashMap as the default implementation (LRU strategy)..
- Add a `ParameterMetric` class as frequent parameter metrics for a specific resource. The metric map is located in `ParamFlowSlot` rather than `ClusterNode`.
- Implement `ParameterLeapArray` as statistic data structure for frequent parameters in a period of time window.
- Add `ParamFlowSlot` as the checker slot; Add `ParamFlowChecker` to do rule checking; Add `ParamFlowRuleManager` to do rule managing.
- The statistic metrics for frequent parameters is enabled only if the related resource has configured parameter flow rule; Parameter metrics for removed rules will be cleared automatically.
- Leverage extensible `SlotChainBuilder` to provide a `HotParamSlotChainBuilder`.
- Add command handlers for hot param rules.
- Add test cases and demo.