Bump GITLAB_KAS_VERSION to 14.9.0

What does this MR do and why?

Monthly version bump. Highlights from the KAS side this milestone:

• Support UID in impersonation client
• Resolve Starboard vulnerabilities after scan

For the full list of changes, see gitlab-org/cluster-integration/gitlab-agent@v14.8.1...v14.9.0 (but note that this also includes changes that do not apply to KAS).

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.