Add 2.7.0 release notes (#652) (#653)

* Add 2.7.0 release notes

Signed-off-by: gaobinlong <gbinlong@amazon.com>

* modify release notes

Signed-off-by: gaobinlong <gbinlong@amazon.com>

---------

Signed-off-by: gaobinlong <gbinlong@amazon.com>
(cherry picked from commit 176278e)

Co-authored-by: gaobinlong <gbinlong@amazon.com>

release-notes/opensearch-notifications.release-notes-2.7.0.0.md

@@ -0,0 +1,16 @@
+## Version 2.7.0.0 2023-04-18
+
+Compatible with OpenSearch 2.7.0
+
+### Maintenance
+* [AUTO] Increment version to 2.7.0-SNAPSHOT ([#636](https://github.com/opensearch-project/notifications/pull/636))
+
+### Infrastructure
+* Fixed build failure due to OSCore xContent changes ([#646](https://github.com/opensearch-project/notifications/pull/646))
+* Remove dashboards ([#640](https://github.com/opensearch-project/notifications/pull/640))
+
+### Bug Fixes
+* Convert empty httpEntity to {} to avoid DeliveryStatus initialization exception ([#648](https://github.com/opensearch-project/notifications/pull/648))
+
+### Documentation
+* Add 2.7.0 release notes ([#652](https://github.com/opensearch-project/notifications/pull/652))