feat(medusa): tracking links (#177)

* fix: creates tracking links on fulfillments

* fix: typo

integration-tests/api/src/services/test-not.js

@@ -0,0 +1,19 @@
+import { NotificationService } from "medusa-interfaces";
+
+class TestNotiService extends NotificationService {
+  static identifier = "test-not";
+   
+  constructor() {
+    super();
+  }
+
+  async sendNotification() {
+    return Promise.resolve();
+  }
+
+  async resendNotification() {
+    return Promise.resolve();
+  }
+}
+
+export default TestNotiService;