Items left to allow merge component in Related Merge Requests

When https://gitlab.com/gitlab-org/gitlab-ce/issues/51862#note_162172477 becomes available, add Items left to allow merge component to related merge requests.

For information on its behavior, check the design specs linked in https://gitlab.com/gitlab-org/gitlab-ce/issues/47007, specifically the Items, states, and tooltips.

Note that it may make sense to turn Related Merge Requests into a Vue component at this time.

Originally this component wouldn't link anywhere, and just show the help cursor when hovering. We currently don't have an anchor for the merge request widget, but if we did, we could link there so the user can get more details about the items left to allow merge:

This is something worth discussing with the FE developer that picks up this issue.