Remove support for Cluster Image Scanning Analyzer

What does this MR do and why?

Describe in detail what your merge request does and why.

We are removing support for the Cluster Image Scanning analyzer with GitLab 15.0 (#356465 (closed)). This change removes the CI templates which are used to run the analyzer, and the security orchestration policies code which is used to create pipelines.

Note that only a small subset of Cluster Image Scanning functionality is being removed. The Cluster Image Scanning feature itself remains a part of GitLab.

• Cluster Image Scanning can still be used via the GitLab Agent
• The cluster_image_scanning job artifacts and vulnerability reports types will remain. Custom integrations can still output cluster_image_scanning reports.

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