mark APPROVED merge requests when viewed in a list

What does this MR do?

Shows APPROVED on an MR list items when viewing projects merge requests (Similar to MERGED and CLOSED)

This MR works as is with the simple assumption that if APPROVED is not there, it may still require approvals.

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

I brought this up in https://gitlab.com/gitlab-org/gitlab-ee/issues/1864, but probably just a review of UI (i.e., should this do more or something different. Should we show a fraction of approvals/approvals_left if there are more approvals waiting?)

I thought I would get the MR up so that gitlab-ee approvers could weigh in on design if wanted #attentionHog

Why was this MR needed?

This was a feature proposal from https://gitlab.com/gitlab-org/gitlab-ee/issues/1864. I believe it really helps workflow when dealing with multiple merge_requests you're following to help quickly decide what might need your attention when viewing a search result or a projects list of MRs.

Ideally, we'd be able to filter approved MRs from unapproved, but that's for another day...

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
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#1864