add 2.8.0 release notes (opensearch-project#500)

Signed-off-by: Kaituo Li <kaituo@amazon.com>

Author: kaituo

release-notes/opensearch-anomaly-detection-dashboards.release-notes-2.8.0.0.md

@@ -0,0 +1,11 @@
+## Version 2.8.0.0 Release Notes
+
+Compatible with OpenSearch Dashboards 2.8.0
+
+### Bug Fixes
+
+* fixing test to pass with node 18 ([#491](https://github.com/opensearch-project/anomaly-detection-dashboards-plugin/pull/491))
+
+### Documentation
+
+* Updating maintainers and code owners ([#476](https://github.com/opensearch-project/anomaly-detection-dashboards-plugin/pull/476))