Adds docs for the standalone vulnerability page

What does this MR do?

This adds documentation for the standalone vulnerabilities page.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• [-] Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

touches #204847 (closed)