Add support for alerts using Apprise

[mariotaddeucci]

Apprise has a support for many message services. This will make the alert support more available for companies that uses teams, discord and other kind of messaging.

Off course not all providers will support all the features that elementary has on its notification but I think it's a good way to make elemetary better for the end user.

Here's the apprise repo: https://github.com/caronc/apprise