setup.py support

What does this MR do?

Implement setup.py support.

We should refactor the code and implement some kind of plugin architecture to avoid repeating the list of the supported dependency files, but this is of the out the scope of this MR.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/11244

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
  • Yes, see gitlab-org/gitlab!16614 (merged)
• [-] 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
  • Yes, tested by adding a setup.py file added to test/fixtures. The result is consistent with the requirements.txt. The file had to be removed because we can't have multiple integration tests in the same project at the same time.
• [-] Job definition updated, if necessary
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• [-] Security reports checked/validated by reviewer