Skip rulesets if path is not configured

What does this MR do?

If report.Config.Path is not set, then the analyzer will emit an error message like:

[ERRO] [cluster-image-scanning] [2021-07-07T12:33:27-05:00] ▶ read /Users/bwilliams/git/cluster-image-scanning: is a directory

Since rulesets are only used by SAST and Secret Detection, the analyzer should allow for this to be unset, and skip trying to filter by rulesets if it is not.

What are the relevant issue numbers?

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