feat: Custom line items (#10408)

* feat: Custom line items

* fix tests

* fix migration

* Allow custom items in update line item workflow

* throw if line item doesn't have a price

* minor things

* wip

* fix flows

* fix test

* add default

* add to type

packages/modules/cart/integration-tests/__tests__/services/cart-module/index.spec.ts

@@ -2512,6 +2512,7 @@ moduleIntegrationTestRunner<ICartModuleService>({
             requires_shipping: true,
             is_discountable: true,
             is_tax_inclusive: false,
+            is_custom_price: false,
             raw_compare_at_unit_price: null,
             raw_unit_price: {
               value: "100",
@@ -2617,6 +2618,7 @@ moduleIntegrationTestRunner<ICartModuleService>({
             requires_shipping: true,
             is_discountable: true,
             is_tax_inclusive: false,
+            is_custom_price: false,
             raw_compare_at_unit_price: null,
             raw_unit_price: {
               value: "200",