Add consolidated release notes for 1.3.18 (opensearch-project#4850)

Signed-off-by: Zelin Hao <[email protected]>

release-notes/opensearch-release-notes-1.3.18.md

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+# OpenSearch and OpenSearch Dashboards 1.3.18 Release Notes
+
+## Release Details
+
+[OpenSearch and OpenSearch Dashboards 1.3.18](https://opensearch.org/versions/opensearch-1-3-18.html) includes the following maintenance updates.
+
+OpenSearch [Release Notes](https://github.com/opensearch-project/OpenSearch/blob/main/release-notes/opensearch.release-notes-1.3.18.md).
+
+
+## MAINTENANCE
+
+### Opensearch Security
+
+
+* Bump bouncycastle to 1.78.1 and kafka to 3.7.0 ([#4437](https://github.com/opensearch-project/security/pull/4437))
+* Bump jose to address CVE ([#4549](https://github.com/opensearch-project/security/pull/4549))