Django sql injection using raw

What does this MR do?

This MR adds Django rule and test cases to cover SQL Injection caused by using raw() method

What are the relevant issue numbers?

Addresses issue : gitlab-org/gitlab#438856 (closed)

Does this MR meet the acceptance criteria?

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