Disable rule mode for unsupported scanners

What does this MR do and why?

Describe in detail what your merge request does and why.

Disable rule mode for unsupported scanners

• in yaml mode, a user can put in whatever they want for the scan property
• rule mode only supports a specific selection of scanners
• disable rule mode if a user puts in a scanner that is not supported
• remove support for cluster_image_scanning in rule mode

Changelog: changed

EE: true

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Page	Before	After
Scan selection
Rule mode with cluster_image_scanning selected

How to set up and validate locally

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

1. Upload a GitLab Ultimate license
2. Navigate to a project => Security & Compliance => Policies => New policy => Scan Execution Policy
3. Try to select cluster_image_scanning
4. Navigate to yaml mode and add cluster_image_scanning and navigate back to rule mode

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 #375493 (closed)