Add support for notification service plugins about snapraid-runner

[fmoledina]

I haven't looked into it too deeply, but I believe Apprise is a single configurable hook-in point, perhaps with a well-defined API for different notification services.

[cfelicio]

If you can integrate apprise, it will take care of pretty much of notification needs: https://github.com/caronc/apprise

Example of a tool using it: https://github.com/dgtlmoon/changedetection.io

[superjkl]

So I've whipped up a quick and dirty fork with apprise support if there's still any interest https://github.com/superjkl/snapraid-runner