Adds 2.16 release notes (#4596)

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>
(cherry picked from commit 77ea464)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

release-notes/opensearch-security.release-notes-2.16.0.0.md

@@ -0,0 +1,41 @@
+## Version 2.16.0 Release Notes
+
+Compatible with OpenSearch and OpenSearch Dashboards version 2.16.0
+
+### Enhancements
+* Add support for PBKDF2 for password hashing & add support for configuring BCrypt and PBKDF2 ([#4524](https://github.com/opensearch-project/security/pull/4524))
+* Use SystemIndexRegistry from core to determine if request contains system indices ([#4471](https://github.com/opensearch-project/security/pull/4471))
+* Separated DLS/FLS privilege evaluation from action privilege evaluation ([#4490](https://github.com/opensearch-project/security/pull/4490))
+* Update PULL_REQUEST_TEMPLATE to include an API spec change in the checklist. ([#4533](https://github.com/opensearch-project/security/pull/4533))
+* Update PATCH API to fail validation if nothing changes ([#4530](https://github.com/opensearch-project/security/pull/4530))
+* Refactor InternalUsers REST API test ([#4481](https://github.com/opensearch-project/security/pull/4481))
+* Refactor Role Mappings REST API test ([#4450](https://github.com/opensearch-project/security/pull/4450))
+* Remove special handling for do_not_fail_on_forbidden on cluster actions ([#4486](https://github.com/opensearch-project/security/pull/4486))
+* Add Tenants REST API test and partial fix ([#4166](https://github.com/opensearch-project/security/pull/4166))
+* Refactor Roles REST API test and partial fix #4166 ([#4433](https://github.com/opensearch-project/security/pull/4433))
+* New algorithm for resolving action groups ([#4448](https://github.com/opensearch-project/security/pull/4448))
+* Check block request only if system index ([#4430](https://github.com/opensearch-project/security/pull/4430))
+* Replaced uses of SecurityRoles by Set<String> mappedRoles where the SecurityRoles functionality is not needed ([#4432](https://github.com/opensearch-project/security/pull/4432))
+
+### Bug Fixes
+* Fixed test failures in FlsAndFieldMaskingTests ([#4548](https://github.com/opensearch-project/security/pull/4548))
+* Typo in securityadmin.sh hint ([#4526](https://github.com/opensearch-project/security/pull/4526))
+* Fix NPE getting metaFields from mapperService on a close index request ([#4497](https://github.com/opensearch-project/security/pull/4497))
+* Fixes flaky integration tests ([#4452](https://github.com/opensearch-project/security/pull/4452))
+
+### Maintenance
+* Remove unused dependancy Apache CXF ([#4580](https://github.com/opensearch-project/security/pull/4580))
+* Remove unnecessary return statements ([#4558](https://github.com/opensearch-project/security/pull/4558))
+* Pass set to SystemIndexRegistry.matchesSystemIndexPattern ([#4569](https://github.com/opensearch-project/security/pull/4569))
+* Refactor and update existing ml roles ([#4151](https://github.com/opensearch-project/security/pull/4151))
+* Replace JUnit assertEquals() with Hamcrest matchers assertThat() ([#4544](https://github.com/opensearch-project/security/pull/4544))
+* Update Gradle to 8.9 ([#4553](https://github.com/opensearch-project/security/pull/4553))
+* Bump org.checkerframework:checker-qual from 3.44.0 to 3.45.0 ([#4531](https://github.com/opensearch-project/security/pull/4531))
+* Add security analytics threat intel action  ([#4498](https://github.com/opensearch-project/security/pull/4498))
+* Bump kafka_version from 3.7.0 to 3.7.1 ([#4501](https://github.com/opensearch-project/security/pull/4501))
+* Bump org.junit.jupiter:junit-jupiter from 5.10.2 to 5.10.3 ([#4503](https://github.com/opensearch-project/security/pull/4503))
+* Bump com.fasterxml.woodstox:woodstox-core from 6.6.2 to 6.7.0 ([#4483](https://github.com/opensearch-project/security/pull/4483))
+* Bump jjwt_version from 0.12.5 to 0.12.6 ([#4484](https://github.com/opensearch-project/security/pull/4484))
+* Bump org.eclipse.platform:org.eclipse.core.runtime from 3.31.0 to 3.3.1.100 ([#4467](https://github.com/opensearch-project/security/pull/4467))
+* Bump spring_version from 5.3.36 to 5.3.37 ([#4466](https://github.com/opensearch-project/security/pull/4466))
+* Update to Gradle 8.8 ([#4459](https://github.com/opensearch-project/security/pull/4459))