🛡️ Sentinel: [HIGH] Fix SSRF vulnerability in plugin download

[mttmcknn]

🚨 Severity: HIGH
💡 Vulnerability: The plugin manager passed untrusted user-provided URLs (via addFromDirectURL and addScriptPlugin) directly to http.Get(). While URL schemes were restricted to http and https, the resolved IP addresses were not verified. This allowed an attacker to supply a URL that resolves to a sensitive cloud metadata IP address (e.g., 169.254.169.254), leading to a Server-Side Request Forgery (SSRF) vulnerability.
🎯 Impact: An attacker could coerce the application into making unauthorized HTTP requests to internal cloud provider endpoints, potentially leaking temporary credentials, instance metadata, or other sensitive configuration details.
🔧 Fix: Replaced http.Get() with a custom http.Client (createSafeClient()). This client utilizes a net.Dialer with a Control hook that intercepts the connection after DNS resolution but before the socket is dialed. The hook parses the resolved IP address and explicitly blocks connections to known cloud metadata IP ranges (169.254.169.254).
✅ Verification: The fix can be verified by running go test ./... to ensure no regressions, and by manually providing a URL to the plugin manager that resolves to 169.254.169.254; the request should immediately fail with a "blocked cloud metadata IP" error before any data is sent.

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PR created automatically by Jules for task 16066449967481407555 started by @himattm

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