Security 8.17.9 release notes

[natasha-moore-elastic]

Generate the 8.17.9 release notes for Security and Endpoint, and publish them before or on the release day.

• Feature freeze: Tue, July 8 2025
• Merge release notes by: Mon, July 14 2025
• Anticipated release date: Tue, July 15 2025
• Docs release issue: https://github.com/elastic/dev/issues/3206

To-do

• Draft the release notes
• Add the release notes PR to the docs release issue
• Known issues:
  • Carry forward known issues that haven't been fixed yet
  • Update the summaries of known issues that were fixed in the current release (add fix details)
  • Document new known issues
• Merge the Security release notes PR