title: Flask BackgroundScheduler running in multiple workers
body: <p>I have the following code</p>
  
  <pre><code>INTERVAL = 30  # in seconds
  scheduler = BackgroundScheduler(
      executors={'default': ThreadPoolExecutor(1)})
  scheduler.start()
  scheduler.add_job(
      func=import_from_folder,
      trigger=IntervalTrigger(seconds=INTERVAL),
      id='importer_job',
      name='Importer',
      replace_existing=True)
  
  # Shut down the scheduler when exiting the app
  atexit.register(lambda: scheduler.shutdown())
  </code></pre>
  
  <p>My app has 4 workers, which makes the above Scheduler run 4 times.
  Is there a way to force the Scheduler to run only in 1 worker ?? or to verify if the scheduler id is already runing in another worker ?</p>