WIP: Add links to Admin Area overview features and components

What does this MR do?

Add links to Admin Area dashboard where applicable (/admin).

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

Not that I am aware of. Double-check missing links not covered in issue.

Why was this MR needed?

Covers https://gitlab.com/gitlab-org/gitlab-ee/issues/4149.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by 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
• Conform by the merge request performance guides
• Conform by the style 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?

Closes #4149 (moved)