apprise notification support

[drosoCode]

Replace the pushbullet notifications by apprise.
With this, over 50 notification services are supported, including pushbullet and discord.
You can configure it using the appriseUrl field in the config.json file with a notification url see here
As python is required, I think that it would be better to offer this optionnal feature as another tag on the docker image.

[jackblk]

Looks cool, this will increase the Docker image size a bit, so I will support a separate docker image with tag 1.5.6-apprise if it is merged.

[Revadike]

Thanks for your contribution!

[jackblk]

@ffuubarbuzz @drosoCode
I tested and did some comparision in #144. I decided to keep apprise image separated from the normal image.

You can start to use apprise before 1.5.6 release from here: docker pull ghcr.io/jackblk/epicgames-freebies-claimer:latest-apprise

From 1.5.6, there will be 1.5.6-apprise image if you want to pin down the version.