UpdateTrack extension type

A track to check for updates on.

In addition to the predefined tracks, you can also specify your own track names by creating an instance of UpdateTrack with a custom string value.

For example, if you have a custom track named "my_custom_track", you can create a patch on that track:

  shorebird patch android --track my_custom_track

And then check for updates on that track in your app:

 final status = checkForUpdate(track: UpdateTrack('my_custom_track'));