title: Flutter - How can I create an Incoming Call Notification?
body: <p>I'm building an app that allows users to call eachother using the agora_rtc_engine.
  I'm currently stuck trying to implement a notification system that will alert users when they receive a call.</p>
  
  <p>I'm using Firebase Messaging for notifications. </p>
  
  <p>I have the following questions:</p>
  
  <ol>
  <li><p>How would I go about replacing the default notification card with a custom one that has buttons for answering or declining the call?</p></li>
  <li><p>How can I specify the amount of time the notification stays on screen? An incoming call rings for about 30 seconds before closing, so I would like my notification card to appear on screen for that period of time.</p></li>
  </ol>
  
  <p>I've been looking at the flutter_local_notifications, but they don't have a "incoming call" notification style.</p>
  
  <p>Any piece of information is highly appreciated. Thank you!</p>