feat(core-flows, fulfillment): Add create return specific method and add more tests (#7357)

* feat(core-flows, fulfillment): Add create return specific method and add more tests

* fix defautl providers in tests fixtures

* more tests

* wip fixes

* fix flow and tests

* cleanup

packages/modules/fulfillment/integration-tests/__fixtures__/providers/default-provider.ts

@@ -14,6 +14,10 @@ export class FulfillmentProviderServiceFixtures extends AbstractFulfillmentProvi
   async getFulfillmentOptions(): Promise<any> {
     return {}
   }
+
+  async createReturnFulfillment(fulfillment): Promise<any> {
+    return {}
+  }
 }
 
 export const services = [FulfillmentProviderServiceFixtures]