code: def total_amount(qs) -> Total:
      
      aggregate = qs.values('amount_currency').annotate(sum=Sum('amount'))
      return Total(Money(amount=r['sum'], currency=r['amount_currency']) for r in aggregate)
docs: Sums the amounts of the objects in the queryset, keeping each currency separate.
      :param qs: A querystring containing objects that have an amount field of type Money.
      :return: A Total object.