Merge notifications of the same type

[canny]

If three people recently favorited the same post, then have one single consolidated notification that says "[Username] and 2 others favorited your toot."

Boosts, favorites, and follows can all be consolidated.

https://tooot.canny.io/admin/board/feature-requests/p/merge-notifications-of-the-same-type

[canny]

This issue has been linked to a Canny post: Merge notifications of the same type 🎉