Add 2.18 release notes (#1347) (#1348)

(cherry picked from commit da73506)

Signed-off-by: Tyler Ohlsen <ohltyler@amazon.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

release-notes/opensearch-anomaly-detection.release-notes-2.18.0.0.md

@@ -0,0 +1,13 @@
+## Version 2.18.0.0 Release Notes
+
+Compatible with OpenSearch 2.18.0
+
+### Enhancements
+* Add rule validation in AnomalyDetector constructor ([#1341](https://github.com/opensearch-project/anomaly-detection/pull/1341))
+
+### Bug Fixes
+* Bump RCF Version and Fix Default Rules Bug in AnomalyDetector ([#1334](https://github.com/opensearch-project/anomaly-detection/pull/1334))
+
+### Infrastructure
+* forward port flaky test fix and add forecasting security tests ([#1329](https://github.com/opensearch-project/anomaly-detection/pull/1329))
+* Updating several dependencies ([#1337](https://github.com/opensearch-project/anomaly-detection/pull/1337))