Changes the data model for counts on the Group Security Dashboard

What does this MR do?

!8972 (merged) introduced a change to the way data is returned for the group security dashboard. Intead of returning data like this:

{
  "sast": {
     "critical": 2,
     "high": 4,
     "low": 7,
     "medium": 8,
     "unknown": 9
  },
  "dependency_scanning": {
     "critical": 2,
     "high": 3,
     "low": 9,
     "medium": 4,
     "unknown": 7
  },
}

We just get data based on our filters, like this:

{
   "critical": 2,
   "high": 4,
   "low": 7,
   "medium": 8,
   "unknown": 0
}

This MR fixes the frontend so it can parse the new data format correctly.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• [ x Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer