Support for Apprise notifications

[Zedjones]

I would love to be able to use my already running Gotify instance for notifications.
Rather than implement notifications in a bespoke way, it might make sense to integrated with a system like Apprise.

It's got a CLI that you can just include in the container and call with the specified URI when notifications need to be sent.

If you need help implementing this feature, I can probably make a PR.

[niondir]

I would prefer some way to include some custom .sh script "Hooks" that one can configure to run. There you can add any 3rd party related logic you need.
The container it self should stay clean from too many 3rd party services / programs.