[Feature] Implement Discord Webhook Provider

[mijinummi]

Title: [Feature] Implement Discord Webhook Provider in /libs/notify

📝 Description

We need a standard integration for Discord alerts. Sentinel currently detects threats but needs a way to push those alerts to a user's Discord server using Webhooks.

🎯 Goal

Create a discord.provider.ts file in the /libs/notify directory that handles the POST request to a Discord Webhook URL.

✅ Requirements

• Create an interface for Alert Payloads (Title, Description, Severity).
• Use axios or node-fetch to send the payload to Discord.
• Include basic error handling if the Webhook URL is invalid.

🛠 Technical Specs

• Difficulty: Easy
• Labels: good-first-issue, feature, notifications