Add notification handlers for backup and patch failures

[gelihub]

To further improve operational safety and awareness in the Warewulf patch playbook:

• Add handlers that notify admins (e.g., via email or logging) when rclone backup or yum update fails.
• Document how to configure notification options (mail, Slack, etc.).
• Ensure failure messages contain relevant context, such as which image failed and the reason.

This will help admins respond more quickly to issues during automated patching.