Move counter on related merge requests/issues into a badge

Problem to solve

We currently use a UI element that looks like a disabled button for the counter of related merge requests/issues. This is not consistent with how we do counters in many other spaces, and also leads to some confusion where this button would lead if it was clickable.

Proposal

Instead, we could move towards a badge for the counter.

Before	After

/cc @uhlexsis @mikelong Would love to hear what you think about this idea 🙂