UnifiedPush Support

UnifiedPush (https://unifiedpush.org/) is a decentralized push notification system. It would be nice if Pushover had support to use it as an alternative to Apple's or Google's push notification systems.

This would allow even more devices to receive push notifications as applications with support for UnifiedPush are developed, provides an alternative for privacy-focused users, and helps avoid vendor lock-in to Apple's and Google's ecosystems.