Add badge count for groups

The following discussion from !18425 (merged) should be addressed:

• @godfat started a discussion: (+13 comments)

  This can be wrong: ...

In !18425 (merged), we've added badge count for projects. The plan was to also add a badge count for groups (see screenshot below) but this requires a concrete plan for further changes in the BE. See the discussion above for more details.

Screenshots

Projects badge count (DONE)	Groups badge count (PENDING)