Adding 2.6 release notes (#388)

Signed-off-by: Sagar Upadhyaya <sagar.upadhyaya.121@gmail.com>
(cherry picked from commit 7c32918)

release-notes/opensearch-performance-analyzer.release-notes-2.5.0.0.md

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+## Version 2.5.0 Release Notes
+
+Compatible with OpenSearch 2.5.0
+
+### Bug fixes
+* Add Connection read timeout to prevent indefinite wait ([#354](https://github.com/opensearch-project/performance-analyzer/pull/354))
+
+### Maintenance
+* Upgrade netty to 4.1.86 ([#352](https://github.com/opensearch-project/performance-analyzer/pull/352))
+* Update jackson to 2.14.1 ([#369](https://github.com/opensearch-project/performance-analyzer/pull/369))
+

release-notes/opensearch-performance-analyzer.release-notes-2.6.0.0.md

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+## Version 2.6.0 Release Notes
+
+Compatible with OpenSearch 2.6.0
+
+### Features
+* Cluster config api return verbose PA status ([#342](https://github.com/opensearch-project/performance-analyzer/pull/342))
+
+### Bug Fixes
+* Fix ShardEvents and ShardBulkDocs null metrics ([#283](https://github.com/opensearch-project/performance-analyzer-rca/pull/283))
+* Fix and include unauthenticated user web server test ([#273](https://github.com/opensearch-project/performance-analyzer-rca/pull/273))
+
+### Maintenance
+* upgrade guava,protobuf minor versions ([#375](https://github.com/opensearch-project/performance-analyzer/pull/375))
+* update jackson ([#370](https://github.com/opensearch-project/performance-analyzer/pull/370))
+* Pin bcel version to 6.6.1 ([#270](https://github.com/opensearch-project/performance-analyzer-rca/pull/270))