add support for background downloading

[indrastorms]

Problem: while downloading a big media file and want to download in the background the download pauses, it only downloads while running it in the foreground. Note: Battery optimisation is turned off for this app.

Solutions: while downloading any file push a persist android notification. So, users can track the progress from anywhere, and also android will not kill the progress (you know android kills the process even if the battery optimization is turned off)

Android: 13