Implement foreground verification of CI artifacts (EE)

What does this MR do?

EE version of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17578

In addition to cherry-picking the commit there, it:

• Restricts the artifacts to those without object storage
• Moves some EE-only files around to make the directory tree logically coherent

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

By itself, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17578 would break EE.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17578