fix(medusa): quantity prices for line item updates (#5137)

* initial code push

* update metadata and only merge if the existing line item allows merging

* update should_merge check

* undo changes to taxrate service

* update results with unit pricing corresponding to the db values after update

* add should_merge property to line_item creation

* add should_merge property to line_item creation

* fix unit tests

* undo adding "should_merge" to create-line-item

* undo change to "addOrUpdateLineItem"

* :wqh_merge from generate method

* undo changes to unit tests

* revert to adding pricing in updateLineItem method

* update cart service test

* Create funny-radios-juggle.md

---------

Co-authored-by: Oli Juhl <59018053+olivermrbl@users.noreply.github.com>

integration-tests/helpers/cart-seeder.js

@@ -531,6 +531,33 @@ module.exports = async (dataSource, data = {}) => {
     variant_id: "test-variant-quantity",
   })
 
+  const quantityVariant1 = manager.create(ProductVariant, {
+    id: "test-variant-quantity-1",
+    title: "test variant quantity 1",
+    product_id: "test-product",
+    inventory_quantity: 1000,
+    options: [
+      {
+        option_id: "test-option",
+        value: "Fit",
+      },
+    ],
+  })
+
+  await manager.save(quantityVariant1)
+
+  await manager.insert(MoneyAmount, {
+    id: "test-price_quantity-1.5",
+    currency_code: "usd",
+    amount: 950,
+  })
+
+  await manager.insert(ProductVariantMoneyAmount, {
+    id: "pvma-quantity-1.5",
+    money_amount_id: "test-price_quantity-1.5",
+    variant_id: "test-variant-quantity-1",
+  })
+
   await manager.insert(MoneyAmount, {
     id: "test-price_quantity-2",
     currency_code: "usd",