Add flawfinder-rulesets.

What does this MR do?

This MR contains a yaml file that contains flawfinder(c) rulesets which can be detected by Semgrep.

We are currently using the docker image of this project in the rule-testing project. Corresponding to this MR, where we are integrating Flawfinder into the testing framework, the semgrep_flawfinder job fails as this project doesn't have any flawfinder(c) rulesets yet.

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