Release sssd-2.9.9

[sssd-bot]

These are automatically generated release notes for sssd-2.9.9.

Please review and edit the notes before merging.

You can push changes to this pull request

git remote add sssd-bot git@github.com:sssd-bot/sssd.io.git
git fetch sssd-bot refs/heads/SSSD-sssd.io-relnotes-2.9.9
git checkout SSSD-sssd.io-relnotes-2.9.9
git push sssd-bot SSSD-sssd.io-relnotes-2.9.9 --force

[gemini-code-assist]

Code Review

This pull request introduces the release notes for SSSD version 2.9.9 and updates the main releases index. The release notes highlight a security fix for CVE-2026-6245, enhancements to PAM GSSAPI indicators, and improved handling of Active Directory Foreign Security Principals. Review feedback identifies several typos in the changelog, suggests standard reStructuredText formatting for option names, and recommends reordering the release list to maintain a consistent descending version sequence.