fix(utils,medusa,order,cart): fix totals when promotions are included (#9014)

* fix(utils): fix totals when promotions are included

* chore: update totals calc

* chore: ignore taxes when taxable amount is 0

* chore: use subtotals everywhere

* chore: fix shipping totals + tests

packages/medusa/src/api/store/carts/query-config.ts

@@ -9,6 +9,7 @@ export const defaultStoreCartFields = [
   "subtotal",
   "tax_total",
   "discount_total",
+  "discount_subtotal",
   "discount_tax_total",
   "original_total",
   "original_tax_total",

packages/medusa/src/api/store/orders/query-config.ts

@@ -26,6 +26,7 @@ export const defaultStoreRetrieveOrderFields = [
   "subtotal",
   "tax_total",
   "discount_total",
+  "discount_subtotal",
   "discount_tax_total",
   "original_total",
   "original_tax_total",