Warn on failure
## What does this MR do?
Adds styling and HTML for a `success_with_warnings` status in the MR widget. Unfinished as it needs some plumbing in the relevant CI controllers and models.
## Are there points in the code the reviewer needs to double check?
Not at the moment, though I think I'll probably need help getting this to work in the backend.
## What are the relevant issue numbers?
#17669
## Screenshots (if relevant)
## Does this MR meet the acceptance criteria?
- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
- [ ] Added for this feature/bug
- [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
cc: @ayufan
See merge request !5004
