Add MetricsRepository interface and reuse original in-memory implementation

[sczyh30]

Describe what this PR does / why we need it

Add MetricsRepository interface and reuse original in-memory implementation.

Does this pull request fix one issue?

Closes #69

Describe how you did it

• Abstract a universal MetricsRepository interface so that users can implement their own metrics persistence.
• Reuse original in-memory implementation (InMemoryMetricsRepository) as the default repository.

[codecov-io]

Codecov Report

Merging #126 into master will increase coverage by 1.1%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #126     +/-   ##
===========================================
+ Coverage     45.67%   46.77%   +1.1%     
- Complexity      554      562      +8     
===========================================
  Files           114      114             
  Lines          3814     3814             
  Branches        531      531             
===========================================
+ Hits           1742     1784     +42     
+ Misses         1859     1808     -51     
- Partials        213      222      +9

Impacted Files	Coverage Δ	Complexity Δ
...a/csp/sentinel/slots/statistic/base/LeapArray.java	76.92% <0%> (+5.12%)	15% <0%> (+1%)	⬆️
...ibaba/csp/sentinel/eagleeye/EagleEyeLogDaemon.java	30.3% <0%> (+6.06%)	6% <0%> (+1%)	⬆️
...a/csp/sentinel/slots/statistic/base/LongAdder.java	31.91% <0%> (+14.89%)	10% <0%> (+6%)	⬆️
...ba/csp/sentinel/slots/statistic/base/Stripe64.java	56.25% <0%> (+30.2%)	0% <0%> (ø)	⬇️

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[yfh0918]

目前InMemoryMetricsRepository是默认实现，后期如果自己增加实现的话，需要实现MetricsRepository接口，但是会存在两种实现，MetricController.java里面是否可以把MetricsRepository metricStore -> List<MetricsRepository metricStore> metricStoreList,后面的部分判断下metricStoreList的size如果=1 就用InMemoryMetricsRepository，如果 > 1就用另外一个

[sczyh30]

Hi, I think just a single MetricsRepository is enough. If users want to use their own implementation, just register as a bean, and then add a @Qualifier annotation on the MetricsRepository field indicating their own implementation.

[CarpenterLee]

LGTM