add an id string argument for the system

src/entities/InterchangeSystem.ts

@@ -8,12 +8,22 @@ import { ShuttleGetterSetterRepository } from "../repositories/ShuttleGetterSett
 
 export interface InterchangeSystemBuilderArguments {
   name: string;
+
+  /**
+   * ID to identify the system internally and in the API.
+   */
+  id: string;
+
+  /**
+   * ID for fetching shuttle data from the Passio GO! system.
+   */
   passioSystemId: string;
 }
 
 export class InterchangeSystem {
   constructor(
     public name: string,
+    public id: string,
     public shuttleDataLoader: ShuttleRepositoryLoader,
     public shuttleRepository: ShuttleGetterSetterRepository,
     public notificationScheduler: ETANotificationScheduler,
@@ -38,6 +48,7 @@ export class InterchangeSystem {
 
     return new InterchangeSystem(
       args.name,
+      args.id,
       shuttleDataLoader,
       shuttleRepository,
       notificationScheduler,