Use expedited tasks when behind on motion videos

[jkaczman]

Android takes a long time by default to process motion videos in the backgrounds. On a Pixel 7, roughly 80 seconds to decrypt one. This can lead to taking really long to download everything if there's a build up. To get around this, we can detect how many behind we are (via the server), and if necessary, schedule an expedited task to take care of it. See https://developer.android.com/develop/background-work/background-tasks/persistent/getting-started/define-work#expedited for details regarding Android's expedited background work.

This will need to be implemented via work manager plugin, see https://github.com/search?q=repo%3Afluttercommunity%2Fflutter_workmanager%20expedited&type=code