feat: return shipping and flow (#125)

Adds support for return shipping methods and changes returns to have a request/receive flow. Store operators should now first request a return, noting the line items that will be returned. When the inventory is received the return will be registered triggering the refund. Return shipping methods can now be created for all regions.

packages/medusa-interfaces/src/fulfillment-service.js

@@ -63,6 +63,37 @@ class BaseFulfillmentService extends BaseService {
   createOrder() {
     throw Error("createOrder must be overridden by the child class")
   }
+
+  /**
+   * Used to retrieve documents associated with a fulfillment.
+   * Will default to returning no documents.
+   */
+  getFulfillmentDocuments(data) {
+    return []
+  }
+
+  /**
+   * Used to create a return order. Should return the data necessary for future
+   * operations on the return; in particular the data may be used to receive
+   * documents attached to the return.
+   */
+  createReturn(fromData) {
+    throw Error("createReturn must be overridden by the child class")
+  }
+
+  /**
+   * Used to retrieve documents related to a return order.
+   */
+  getReturnDocuments(data) {
+    return []
+  }
+
+  /**
+   * Used to retrieve documents related to a shipment.
+   */
+  getShipmentDocuments(data) {
+    return []
+  }
 }
 
 export default BaseFulfillmentService