feat: Add exchange return shipping (#8108)

* wip

* finalize tests

* feat: Add exchange return shipping

* add shipping to preview

* test input

* move utils and ignore already inserted shipping method

* use custom price

---------

Co-authored-by: Carlos R. L. Rodrigues <rodrigolr@gmail.com>

integration-tests/http/__tests__/returns/returns.spec.ts

@@ -225,21 +225,11 @@ medusaIntegrationTestRunner({
           adminHeaders
         )
 
-        expect(result.data.return).toEqual(
+        expect(result.data.order.shipping_methods[1]).toEqual(
           expect.objectContaining({
-            id: expect.any(String),
-            order_id: order.id,
-            display_id: 1,
-            order_version: 2,
-            status: "requested",
-            items: [],
-            shipping_methods: [
-              expect.objectContaining({
-                amount: 1000,
-                name: "Return shipping",
-                shipping_option_id: returnShippingOption.id,
-              }),
-            ],
+            amount: 1000,
+            name: "Return shipping",
+            shipping_option_id: returnShippingOption.id,
           })
         )