add additional method to get shuttles by route

src/unoptimizedInMemoryRepository.ts

@@ -41,6 +41,10 @@ export class UnoptimizedInMemoryRepository implements Repository {
     return this.shuttles.filter(shuttle => shuttle.systemId === systemId);
   }
 
+  public async getShuttlesByRouteId(routeId: string) {
+    return this.shuttles.filter(shuttle => shuttle.routeId === routeId);
+  }
+
   public async getShuttleById(shuttleId: string) {
     return this.findEntityById(shuttleId, this.shuttles);
   }