Parse npm-shrinkwrap.json

What does this MR do?

Add npm-shrinkwrap.json to the files parsed by the existing npm parser.

Prior to this MR the npm parser only parsed package-lock.json files, even though both package-lock.json and npm-shrinkwrap.json share the same format.

What are the relevant issue numbers?

See https://gitlab.com/gitlab-org/gitlab-ee/issues/10075#note_173299300

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
• Publish a new version of main Dependency-Scanning to update dependency file detection