Support Apprise notifications

[claabs]

I think Apprise ( https://github.com/caronc/apprise ) would be a good. I fancy the API ( https://github.com/caronc/apprise-api ) rather than a full version of Apprise. But adding this would give access to over 70 notification services.

Originally posted by @LilTrublMakr in #173 (comment)

[LilTrublMakr]

I have it setup in my config, but is there a way to test the notifications? I am getting errors purchasing this weeks game but I am not getting any notifications about it in either email or through Apprise.

[claabs]

"testNotifiers": true,

https://github.com/claabs/epicgames-freegames-node#testing-notification-and-webserver