Notifiers

Hello, I come from using [Blacbox](https://github.com/lemonsaurus/blackbox) and a feature I am missing from there is the [notifiers](https://github.com/lemonsaurus/blackbox#notifiers) functionality. Basically, being able to post to a Discord webhook with a backups status.

No file, test, or entry point is named. Start by locating how backup status is produced and how configuration is handled, then review the referenced Blackbox notifiers behavior. Done should mean that the requested backup-status notification behavior is implemented and verified, with its configuration and supported notification scope documented.

Written by the indexing model from the issue text.