[FEATURE] Support unifiedpush notifications

[jm355]

Is your feature request related to a problem? Please describe.

UnifiedPush is supported by a lot of foss projects, like moshidon and other mastidon clients, element/matrix clients, and molly-up for signal. It would be cool if alovoa could use that for people who have it set up

Describe the solution you'd like

Option to use unifiedpush for notifications

Describe alternatives you've considered

usually the only alternative is google play services, the app implementing it's own background listener or checking periodically, or no notifications