Adding release notes for 2.8.0 (#471) (#472)

* Adding release notes for 2.8.0

* add release notes for pa-rca

---------

Co-authored-by: Chenyang Ji <cyji@amazon.com>
(cherry picked from commit 74c2939)

Co-authored-by: Chenyang Ji <chenyang.yale@gmail.com>

release-notes/opensearch-performance-analyzer.release-notes-2.8.0.0.md

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+## Version 2.8.0 Release Notes
+
+Compatible with OpenSearch 2.8.0
+
+## Enhancements
+* Add Latency and Error service metrics in PA plugin [#442](https://github.com/opensearch-project/performance-analyzer/pull/442)
+* Add Latency Metrics for respective Emitters in Reader Event Processing [#364](https://github.com/opensearch-project/performance-analyzer-rca/pull/364)
+* Adding Collector Metrics and refactoring the Error metrics [#365](https://github.com/opensearch-project/performance-analyzer-rca/pull/365)
+
+### Bug fixes
+* Fix ShardStateCollector which was impacted by [core refactoring](https://github.com/opensearch-project/OpenSearch/pull/7301) [445](https://github.com/opensearch-project/performance-analyzer/pull/445)
+
+
+### Infrastructure
+* Upgrade gradle to 7.6.1, upgrade gradle test-retry plugin to 1.5.2. ([#438](https://github.com/opensearch-project/performance-analyzer/pull/438))
+* Introduce protobuf and guava dependency from core versions file [#437](https://github.com/opensearch-project/performance-analyzer/pull/437)
+* Update dependency org.xerial:sqlite-jdbc to v3.41.2.2 [#375](https://github.com/opensearch-project/performance-analyzer-rca/pull/375)
+
+
+### Maintenance
+* Update RestController constructor for tests [#440](https://github.com/opensearch-project/performance-analyzer/pull/440)
+* Dependencies change in favor of Commons repo [#448](https://github.com/opensearch-project/performance-analyzer/pull/448)
+* WriterMetrics and config files dependency redirection [#450](https://github.com/opensearch-project/performance-analyzer/pull/450)
+* Refactor code related to Commons change, fixing unit tests [#451](https://github.com/opensearch-project/performance-analyzer/pull/451)
+* Remove remaining dependencies from PA-RCA due to commons repo [#453](https://github.com/opensearch-project/performance-analyzer/pull/453)
+* Fix BWC Integration tests [#413](https://github.com/opensearch-project/performance-analyzer/pull/413)
+* Fix SHA update for PA-Commons repo in build.gradle  [#454](https://github.com/opensearch-project/performance-analyzer/pull/454)
+* Refactor Service/Stat Metrics [#376](https://github.com/opensearch-project/performance-analyzer-rca/pull/376)