Allow client-side encrypted backups for Android app

[Nazar Mokrynskyi]

Basically this: https://github.com/seedvault-app/seedvault/wiki/FAQ#why-do-some-apps-not-allow-to-get-backed-up

I'm moving to non-rooted ROM for the first time in many years (GrapheneOS) and it is a major pain to configure all the apps manually when apps deliberately disable backups in their apps.

According to following example provided it is trivial to do: https://github.com/grote/Transportr/commit/4dc38f429f75909a088d8bd8a5b3b5ddd8030f71

-- 
Sincerely, Nazar Mokrynskyi
github.com/nazar-pc