Compare agent version against KAS version

What does this MR do and why?

On GitLab.com, the GitLab version is almost always ahead of the KAS version, but it is actually the KAS version that we care about.

This is not a complete fix, because on GitLab.com, the KAS version is not determined by GITLAB_KAS_VERSION because we don't have automatic deployments for KAS yet. But it is a more precise estimate than the GitLab version, and will be mostly correct once the KAS version is determined from that file (due to incremental rollouts, canary etc, there is never a guaranteed "one true version").

For self-managed, the problem will never show unless we forget to release a new KAS version.

See #361786 (closed)

Screenshots or screen recordings

Notice the lack of warning in GDK:

GitLab.com	GDK with the fix

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.