Add support for unified push

[ne20002]

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

As of version 19 Tusky will support unified push (see https://unifiedpush.org). It would be great if Friendica would support this.

Describe the feature you'd like

Have a setting to enable use of unified push
Have a configuration to choose unfied push provider

With Nextpush setting up a own unified push provider is easy. It already supports matrix protocol / synapse server and matrix client Element is also adding support. It would be handy to have this for Friendica with Tusky as well. A hope, other foss apps will also implement it.

Describe alternatives you've considered

Additional context

[foss-]

Fedilab also supports unified push. Having an alternative to Google Push is a huge win.

[kr428]

Adding myself here. Currently, fedilab (as maybe the most feature-complete ActivityPub client) doesn't at all seem to be able to display Friendica notifications as they fully focussed on UnifiedPush so essentially using Friendica with fedilab hasn't working (push?) notifications at the moment. Though they also offer sort of a pull notification process, I never managed to get that to work.

[xundeenergie]

There ist https://ntfy.sh as a very well done unified-push and notification server.
I run it for matrix, and it works very well!!