2.19.3 release notes (#5499)

Signed-off-by: Finn Carroll <carrofin@amazon.com>

Author: finnegancarroll

release-notes/opensearch-security.release-notes-2.19.3.0.md

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+## Version 2.19.3 Release Notes
+
+Compatible with OpenSearch and OpenSearch Dashboards version 2.19.3
+
+### Maintenance
+- Bump `com.nimbusds:nimbus-jose-jwt:9.48` from 9.48 to 10.0.2 ([#5480](https://github.com/opensearch-project/security/pull/5480))
+- Bump `checkstyle` from 10.3.3 to 10.26.1 ([#5480](https://github.com/opensearch-project/security/pull/5480))