Enable Support for Rust in Semgrep Analyzer

What does this MR do?

Adds support for Rust (files ending in .rs), following semgrep graduating Rust support to general availability.

What are the relevant issue numbers?

• Support Rust SAST Analyzer (gitlab-org/gitlab#390733)
• Enable Support for Rust in Semgrep Analyzer (gitlab-org/gitlab#439046 - 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 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