Add 2.8 release notes (#794)

* Add 2.8 release notes

Signed-off-by: Xuesong Luo <[email protected]>

release-notes/opensearch-index-management.release-notes-2.8.0.0.md

@@ -0,0 +1,18 @@
+## Version 2.8.0.0 2023-06-06
+
+Compatible with OpenSearch 2.8.0
+
+### Maintenance
+* Upgrade to gradle 8.1.1. ([#777](https://github.com/opensearch-project/index-management/pull/777))
+* Bump version to 2.8. ([#759](https://github.com/opensearch-project/index-management/pull/759))
+
+### Features
+* Support notification integration with long running operations. ([#790, 791, 793](https://github.com/opensearch-project/index-management/pull/793))
+
+### Bug fixes
+* Remove recursion call when checking permission on indices. ([#785](https://github.com/opensearch-project/index-management/pull/785))
+* Added trimming of nanos part of "epoch_millis" timestamp when date_histogram type used is date_nanos. ([#782](https://github.com/opensearch-project/index-management/pull/782))
+* Added proper resolving of sourceIndex inside RollupInterceptor, it's required for QueryStringQuery parsing. ([#773](https://github.com/opensearch-project/index-management/pull/773))
+
+### Documentation
+* Added 2.8 release notes. ([#794](https://github.com/opensearch-project/index-management/pull/794))