Add release notes for 3.4.0

Signed-off-by: opensearch-ci <[email protected]>

Author: opensearch-ci-bot

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

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+## Version 3.4.0 Release Notes
+
+Compatible with OpenSearch and OpenSearch Dashboards version 3.4.0
+
+### Features
+* PPL Alerting: Execute Monitor and Monitor Stats ([#1960](https://github.com/opensearch-project/alerting/pull/1960))
+* PPL Alerting: Get and Search Monitors ([#1966](https://github.com/opensearch-project/alerting/pull/1966))
+* PPL Alerting: Delete Monitor, More V1/V2 Separation ([#1968](https://github.com/opensearch-project/alerting/pull/1968))
+* PPL Alerting: Get Alerts and Alert Lifecycle ([#1972](https://github.com/opensearch-project/alerting/pull/1972))
+
+### Bug Fixes
+* Fix CI check with security failing due to empty string in payload body ([#1994](https://github.com/opensearch-project/alerting/pull/1994))
+
+### Infrastructure
+* Kotlin version upgrade ([#1993](https://github.com/opensearch-project/alerting/pull/1993))
+* JDK upgrade to 25 and gradle upgrade to 9.2 ([#1995](https://github.com/opensearch-project/alerting/pull/1995))