Refactoring Service/Stat Metrics

[khushbr]

Is your feature request related to a problem? Please provide an existing Issue # , or describe. https://github.com/opensearch-project/performance-analyzer-commons/issues/8

Describe the solution you are proposing

• Refactor Service/Stat Metric Codebase
• The emitMetrics Service metric is currently working only for ES versions. All the timers are currently broken for OS version.
• Add Inherent support for service metrics in Collector Framework

Check List

• [ ] New functionality includes testing.
  • [x] All tests pass
• [ ] New functionality has been documented.
  • [ ] New functionality has javadoc added
• [x] Commits are signed per the DCO using --signoff

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[Tjofil]

In commons/stats/eval/impl/vals, subpackages sound generic and don't have much meaning, do we keep them, rename them or flatten them back ?

[khushbr]

In commons/stats/eval/impl/vals, subpackages sound generic and don't have much meaning, do we keep them, rename them or flatten them back ?

We can later revisit and flatten this out. I wanted to keep this consistent with directory structure in RCA package to ensure we don't miss any of the files. The README is also arranged as per the structure, we can update both later.