Add release notes for 3.4.0

Signed-off-by: opensearch-ci <opensearch-infra@amazon.com>

Author: opensearch-ci-bot

release-notes/opensearch-observability.release-notes-3.4.0.0.md

@@ -0,0 +1,7 @@
+## Version 3.4.0 Release Notes
+
+Compatible with OpenSearch and OpenSearch Dashboards version 3.4.0
+
+### Maintenance
+* Upgrade gradle to version 9.2 and Java to version 25 ([#1959](https://github.com/opensearch-project/observability/pull/1959))
+* Bump logback core to 1.15.20 ([#1960](https://github.com/opensearch-project/observability/pull/1960))