Implement `Fully Specced Out` Extended Merge Request Popover
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Follow up issue to https://gitlab.com/gitlab-org/gitlab-ce/issues/54916
| Fully specced out | Ready to merge | Barebones | Skeleton loading |
|-------------------|----------------|-----------|------------------|
|  |  |  |  |
In initial pass, we only did the `Barebones` version of this. There is some work to be done to add statistics and creator/assignee to the bottom
This design adds the following:
- Assignee
- Milestone
- Tasks completed/total
- MR Health
- Originally from https://gitlab.com/gitlab-org/gitlab-ce/issues/47007, this gives a good idea of how far towards being merged a MR is.
- *We wouldn't be showing extra tooltips on top of a tooltip though.*
- 
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