Remove scanner, category fields from vulnerabilities, in Security reports

Summary

After adding .scan.scanner and .scan.type to the security reports as described in #202053 (closed), we should then remove .vulnerabilities[].scanner and .vulnerabilities[].category, for these are redundant.

• remove Category and Scanner struct field from the Issue struct, in the common library, and update the Secure analyzers (SAST, Container Scanning, Secret Detection, and Dependency Scanning)
• update the Rails backend of gitlab
• remove the fields from the JSON schemas, in security-report-schemas (covered in Build and release next MODEL (aka major) versio... (#339812 - closed))

Improvements

The new security reports are smaller and more readable.

Risks

The main risk is to break backward compatibility when running new versions of the Secure analyzers with old versions of the GitLab backend.

Involved components

• Secure analyzers and their common library
• DAST
• security-report-schemas
• gitlab

Optional: Intended side effects

Optional: Missing test coverage