Per-app notifications

[Bastih18]

Consider adding support for per-app notifications, such as the ability to configure Discord Webhooks for specific apps. This would allow users to receive deployment notifications or logs for individual apps, rather than logging all activity across Coolify to a single webhook.

This feature would be particularly useful for scenarios where users want to limit notifications to a specific app. For example, they might only want deployment logs for a particular app to be shared in a public Discord server, without exposing logs or updates for other projects.