Check license before package metadata sync

What does this MR do and why?

This MR ensures that the PackageMetadata::Syncworker runs based on whether the feature is available for the user's license.

Because the worker executes at the instance level this logic checks the instance's license for feature availability.

Quoting the issue:

According to the license model self-managed subscriptions are installed at an instance level and GitLab SaaS is a special self-managed instance that is Ultimate. So it should be enough to check whether the license_scanning feature is available.

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.

Related to #396737 (closed)