Semgrep Service: Single file analysis without scaffolding

What does this MR do?

This MR simplifies single-file analysis by creating a temporary file, run the analysis on the file and return the result. It does not scaffold a project dir structure.

What are the relevant issue numbers?

Related MR: !421 (closed) Related Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/462808

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 updated/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