Update container scanning for registry docs link

What does this MR do and why?

Update container scanning for registry docs link

• Point to container scanning for registry docs

Changelog: fixed

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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

Before	After (no UI change)

How to set up and validate locally

1. Import the https://gitlab.com/gitlab-examples/security/security-reports project or any project that generates vulnerabilities
2. Run pipeline, generate vulnerabilities
3. Navigate to the Vulnerability Report page
4. Click on container registry vulnerabilties tab
5. Observe empty state
6. Click on "How do I enable Container Scanning For Registry?"

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