Creates a retrospective process group

curl --request POST \
  --url https://api.rootly.com/v1/retrospective_processes/{retrospective_process_id}/groups \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '{
  "data": {
    "type": "retrospective_process_groups",
    "attributes": {
      "sub_status_id": "<string>",
      "position": 123
    }
  }
}'

{
  "data": {
    "id": "5afb4a50-3d92-4a35-80bb-6b848fbbf0c4",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "b4c8ad90-2920-4bd3-b089-df6bf151b6dd",
      "sub_status_id": "85a3dc96-ed8e-45ea-967b-80c847b4518f",
      "position": 3,
      "updated_at": "2025-05-29T17:47:32.426-07:00",
      "created_at": "2025-05-29T17:47:32.426-07:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}