Add basic interface and adaptations for Sentinel cluster flow control in sentinel-core

[sczyh30]

Describe what this PR does / why we need it

Add basic interface for Sentinel cluster flow control in sentinel-core, and update rules and checkers for FlowRule and ParamFlowRule to adapt to cluster flow control interface.

Does this pull request fix one issue?

Related to #200 (a sub-task of it)

Describe how you did it

• Add basic interface and entity for Sentinel cluster flow control
• Add a universal TokenService SPI interface for both local flow control and distributed flow control service
• Add TokenResult entity to represent result of acquiring token
• Add ClusterTokenClient as the SPI interface for client of Sentinel cluster flow control
• Update flow / parameter flow rule and checker for cluster mode
  • Add new fields clusterMode and clusterConfig for cluster mode
  • Add ClusterFlowConfig and ParamFlowClusterConfig class for rule config in cluster mode
  • Update FlowRuleChecker and ParamFlowChecker to support cluster mode
• Extract rule util classes for FlowRule and ParamFlowRule

Describe how to verify it

See test cases.

Special notes for reviews

NONE

[codecov-io]

Codecov Report

Merging #257 into master will decrease coverage by 1.93%.
The diff coverage is 23.27%.

@@             Coverage Diff              @@
##             master     #257      +/-   ##
============================================
- Coverage     52.59%   50.65%   -1.94%     
- Complexity      913      923      +10     
============================================
  Files           150      158       +8     
  Lines          5037     5249     +212     
  Branches        720      754      +34     
============================================
+ Hits           2649     2659      +10     
- Misses         2065     2253     +188     
- Partials        323      337      +14

Impacted Files	Coverage Δ	Complexity Δ
.../sentinel/slots/block/flow/FlowRuleComparator.java	57.14% <0%> (-22.86%)	5 <4> (ø)
...p/sentinel/slots/block/flow/ClusterFlowConfig.java	0% <0%> (ø)	0 <0> (?)
...a/csp/sentinel/cluster/log/ClusterStatLogUtil.java	0% <0%> (ø)	0 <0> (?)
.../com/alibaba/csp/sentinel/cluster/TokenResult.java	0% <0%> (ø)	0 <0> (?)
...slots/block/flow/param/ParamFlowClusterConfig.java	0% <0%> (ø)	0 <0> (?)
...ba/csp/sentinel/cluster/TokenServerDescriptor.java	0% <0%> (ø)	0 <0> (?)
...baba/csp/sentinel/cluster/TokenClientProvider.java	0% <0%> (ø)	0 <0> (?)
...libaba/csp/sentinel/slots/block/flow/FlowSlot.java	100% <100%> (ø)	8 <6> (ø)	⬇️
...l/slots/block/flow/param/ParamFlowRuleManager.java	76.19% <100%> (+4.76%)	7 <0> (-19)	⬇️
...csp/sentinel/slots/block/flow/FlowRuleChecker.java	56.6% <11.76%> (-21.18%)	16 <1> (+2)
... and 17 more

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[CarpenterLee]

LGTM