Feat(medusa): handle reservation quantity update for line items (#3484)

**What**
-  Raise exception if a reservation is updated or created to have larger quantity than is unfulfilled for a line-item

Fixes CORE-1249

packages/medusa/src/interfaces/services/inventory.ts

@@ -43,6 +43,8 @@ export interface IInventoryService {
     locationId: string
   ): Promise<InventoryLevelDTO>
 
+  retrieveReservationItem(reservationId: string): Promise<ReservationItemDTO>
+
   createReservationItem(
     input: CreateReservationItemInput
   ): Promise<ReservationItemDTO>