Remove support for the cluster image scanning analyzer

Proposal

• Ensure that users can scan container images running in production through the agent prior to starting this proposal.
• Remove official support for the cluster image scanner analyzer by removing mention of it from GitLab's documentation.
• Make https://gitlab.com/gitlab-org/security-products/analyzers/cluster-image-scanning read only by archiving it.
• Remove any other cluster analyzer scanning code in the main GitLab product.

Implementation plan

• backend Delete lib/gitlab/ci/templates/Security/Cluster-Image-Scanning.gitlab-ci.yml
• backend Remove Security/Cluster-Image-Scanning.gitlab-ci.yml from lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml
• backend Delete ee/app/services/security/security_orchestration_policies/cluster_image_scanning_ci_variables_service.rb and its consumers
• backend Remove Security/Cluster-Image-Scanning from ee/app/services/security/security_orchestration_policies/ci_configuration_service.rb
• documentation Update doc/user/application_security/cluster_image_scanning/index.md to remove analyzer specific content and update agent method of scanning production container images to be a general availability feature.
• Remove the project from Engineering Projects