[Security Rules] Update security rules package to v8.15.16

[tradebot-elastic]

What does this PR do?

Update the Security Rules package to version 8.15.16.
Autogenerated from commit https://github.com/elastic/detection-rules/tree/a6ee1de6de7d0d92973917ea99e27f990c608579

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• If I'm introducing a new feature, I have modified the Kibana version constraint in my package's manifest.yml file to point to the latest Elastic stack release (e.g. ^7.13.0).

Author's Checklist

• Install the most recently release security rules in the Detection Engine
• Install the package
• Confirm the update is available in Kibana. Click "Update X rules" or "Install X rules"
• Look at the changes made after the install and confirm they are consistent

How to test this PR locally

• Perform the above checklist, and use package-storage to build EPR from source

Related issues

None

Screenshots

None

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: df3d608

cc @shashank-elastic

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[elastic-vault-github-plugin-prod]

Package security_detection_engine - 8.15.16 containing this change is available at https://epr.elastic.co/package/security_detection_engine/8.15.16/