Add UI for maven packages feature

What does this MR do?

Adds UI to https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6607

Why was this MR needed?

To reduce size of original merge requests I created UI in separate MR. It adds ability to browse uploaded packages and remove those.

How to test

Follow instructions from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6781#note_92313166

Screenshots (if relevant)

packages index

package show

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• 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-and-qa manual pipeline job)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/5811