Consider show count numbers for SingleRange

**Issue Type:** enhancement

**Platform:** web

**Description:**

I'm a searchkit user, I'm tring to migrate my searchkit project into reactivesearch. reactivesearch is much faster than searchkit!

However, the SingleRange has no count number is not same as searchkit, I think show the aggs of each range, will be a necessary feature (at least its very useful for me and my users), since SingleList could able to show count, but SingleRange couldn't is a little bit weird.

I found here had a similar closed issue #269, a boolean option such as `showCount` will be great, but it still not work in v3.0 now.

Hope this feature could be considered

Best regards