feat: add getAllWorkers method

[anchan828]

#1951

async function bootstrap(): Promise<void> {
  const app = await NestFactory.create(WorkerAppModule);
  const service = app.get(QueueWorkerService);
  const allWorkers = service.getAllWorkers();
  const allProcessors = allWorkers.flatMap(w => w.processors);
 
  // Do somethings...
}