Add dependency files to reports

What does this MR do?

Add a dependency_files key to the JSON reports.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/10071

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
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer