[Backport 2.x] Add release notes for 2.9.0.0

[opensearch-trigger-bot]

Backport f1be2d7 from #2992

[codecov]

Codecov Report

Merging #3026 (b5142dc) into 2.x (109dd27) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #3026      +/-   ##
============================================
+ Coverage     62.30%   62.31%   +0.01%     
+ Complexity     3321     3320       -1     
============================================
  Files           264      264              
  Lines         19468    19468              
  Branches       3326     3326              
============================================
+ Hits          12129    12131       +2     
- Misses         5714     5716       +2     
+ Partials       1625     1621       -4     

see 6 files with indirect coverage changes

[cwperks]

Looking into test failures:

Tests with failures:
 - org.opensearch.security.auditlog.compliance.ComplianceAuditlogTest.testInternalConfig
 - org.opensearch.security.auditlog.compliance.ComplianceAuditlogTest.testComplianceEnable
 - org.opensearch.security.auditlog.compliance.ComplianceAuditlogTest.testUpdate
 - org.opensearch.security.auditlog.compliance.RestApiComplianceAuditlogTest.testBCryptHashRedaction
 - org.opensearch.security.auditlog.compliance.RestApiComplianceAuditlogTest.testBCryptHashRedaction
 - org.opensearch.security.auditlog.compliance.RestApiComplianceAuditlogTest.testAutoInit
 - org.opensearch.security.multitenancy.test.MultitenancyTests.testMultitenancyAnonymousUser
 - org.opensearch.security.multitenancy.test.TenancyPrivateTenantEnabledTests.testPrivateTenantDisabled_Update_EndToEnd
 - org.opensearch.security.auditlog.compliance.ComplianceAuditlogTest.testComplianceEnable
 - org.opensearch.security.auditlog.compliance.ComplianceAuditlogTest.testInternalConfig