Dogfooding: use pre-defined GitLab SAST instead of homemade one

What does this MR do?

Dogfooding: use pre-defined GitLab SAST instead of homemade one.

Confirmed the results at https://gitlab.com/gitlab-org/security-products/analyzers/common/pipelines/112357382/security and once this MR get merged, the report will be available at Security Dashboard: https://gitlab.com/gitlab-org/security-products/analyzers/common/security/dashboard/

What are the relevant issue numbers?

gitlab-org/gitlab#198871 (closed)

Does this MR meet the acceptance criteria?

• [n/a] Changelog entry added
• [n/a] Documentation created/updated for GitLab EE, if necessary
• [n/a] Documentation created/updated for this project, if necessary
• [n/a] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • [n/a] Auto-DevOps template
  • [n/a] Job definition example
  • [n/a] CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer