Refactor the `counts` function in the Group Security Dashboard

We recently changed the way we passed data to the counts on the group security dashboard and can probably remove some complexity from the vulnerability_count_list component as a result.

The following discussion from !9035 (merged) should be addressed:

  • @winh started a discussion: (+2 comments)

    could we move this function to the store? especially the || 0 looks like something that is not specific to this component.

Edited by Sam Beckham