fix(core-flows, link-module): product <> inventory delete cascades (#9528)

**What**
- remove cascade delete of inventory items on product delete
- implement inventory deletion in product/variant delete workflows with checks:
  - product/variant cannot be deleted if there are reservations associated with their inventory items
  - inventory item will be cascade deleted if it's not used by other variants (that are not being deleted in the current flow)

---

FIXES CC-581 CC-582

integration-tests/http/__tests__/inventory/admin/inventory.spec.ts

@@ -782,7 +782,7 @@ medusaIntegrationTestRunner({
       })
 
       describe("DELETE /admin/inventory-items/:id", () => {
-        it("should remove associated levels and reservations when deleting an inventory item", async () => {
+        it("should throw if inventory item with reservations is being removed", async () => {
           await api.post(
             `/admin/inventory-items/${inventoryItem1.id}/location-levels`,
             {
@@ -821,30 +821,16 @@ medusaIntegrationTestRunner({
           ).data
           expect(levelsResponse.count).toEqual(1)
 
-          const res = await api.delete(
-            `/admin/inventory-items/${inventoryItem1.id}`,
-            adminHeaders
+          const res = await api
+            .delete(`/admin/inventory-items/${inventoryItem1.id}`, adminHeaders)
+            .catch((err) => {
+              return err.response
+            })
+
+          expect(res.status).toEqual(400)
+          expect(res.data.message).toEqual(
+            `Cannot remove following inventory item(s) since they have reservations: [${inventoryItem1.id}].`
           )
-
-          expect(res.status).toEqual(200)
-
-          const reservationsResponseAfterDelete = (
-            await api.get(
-              `/admin/reservations?location_id[]=${stockLocation1.id}`,
-              adminHeaders
-            )
-          ).data
-
-          expect(reservationsResponseAfterDelete.count).toEqual(0)
-
-          const levelsResponseAfterDelete = (
-            await api.get(
-              `/admin/inventory-items/${inventoryItem1.id}/location-levels?location_id[]=${stockLocation1.id}`,
-              adminHeaders
-            )
-          ).data
-
-          expect(levelsResponseAfterDelete.count).toEqual(0)
         })
 
         it("should remove the product variant associations when deleting an inventory item", async () => {