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

.changeset/gorgeous-tools-enjoy.md

@@ -0,0 +1,9 @@
+---
+"@medusajs/core-flows": patch
+"@medusajs/cart": patch
+"@medusajs/types": patch
+"@medusajs/utils": patch
+"@medusajs/medusa": patch
+---
+
+chore: Support custom line items