fix: 修复ParameterMetric在生产环境导致的内存泄漏（请求对象继承ParamFlowArgument，包含sku等多个无限…

[love4coding]

…枚举值字段）

Describe what this PR does / why we need it

生产环境dubbo接口配置了热点参数限流规则，请求对象包含sku\店铺id等多个无限枚举值字段，继承ParamFlowArgument指定某个字段配置不同的限流阈值，每隔几天订单服务出现堆内存溢出，服务不可用; 通过分析堆内存，发现ParameterMetric下的HashMap对象在服务启动后逐渐增长达到4g大小，无法gc回收

Does this pull request fix one issue?

NONE

Describe how you did it

ParamFlowArgument.threadCount.CacheMap会为每次dubbo接口的请求的复合请求对象put一组新的健值对, 当dubbo复合请求对象存在无限多个枚举值时, 内存溢出; 优化为只采集ParamFlowArgument指定字段枚举值的线程指标

Describe how to verify it

通过jmter压测或者单测debug ParameterMetric类，每次请求构造不同的arg对象（not equals）, ParamFlowArgument.threadCount.CacheMap每次请求都会put一组新的健值对, 超过默认大小4000后无法及时回收
threadCount.putIfAbsent(arg, new AtomicInteger());

Special notes for reviews

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 45.89%. Comparing base (dbd3c06) to head (9c93754).
Report is 8 commits behind head on 1.8.

Files	Patch %	Lines
...ntinel/slots/block/flow/param/ParameterMetric.java	0.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                1.8    #3391      +/-   ##
============================================
- Coverage     45.90%   45.89%   -0.02%     
+ Complexity     2148     2145       -3     
============================================
  Files           431      431              
  Lines         12906    12910       +4     
  Branches       1728     1730       +2     
============================================
  Hits           5925     5925              
+ Misses         6281     6280       -1     
- Partials        700      705       +5     

Components	Coverage Δ
sentinel-adapter	43.22% <ø> (ø)
sentinel-cluster	23.68% <ø> (-0.11%)	⬇️
sentinel-core	59.58% <ø> (-0.04%)	⬇️
sentinel-extension	46.28% <0.00%> (+0.14%)	⬆️
sentinel-logging	54.54% <ø> (ø)

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