Show number of items in group headings

I checked into the code but couldn't figure out how I would go about showing a number of items in the group (e.g. "Important [42]" as header instead of just "Important"). I originally thought I may be able to use `org-super-agenda-header-prefix`, but didn't see a way to compute the item count as prefix. Perhaps it would be better if it can be a computed suffix, which could be turned on with an extra config?