🛡️ Sentinel: [HIGH] Fix SSRF in plugin manager

[mttmcknn]

🚨 Severity: HIGH
💡 Vulnerability: Server-Side Request Forgery (SSRF). The addFromDirectURL function used http.Get() with user-provided URLs without validating the resolved IP address.
🎯 Impact: An attacker could provide a URL that resolves to the cloud metadata endpoint (169.254.169.254), potentially exposing sensitive cloud credentials or instance metadata.
🔧 Fix: Replaced http.Get() with a custom http.Client and net.Dialer. The dialer uses a Control hook to check the resolved IP after DNS resolution but before the connection is made, explicitly blocking the cloud metadata IP. Also added a 10s timeout to prevent DoS.
✅ Verification: Verified by attempting to download a plugin from http://169.254.169.254/latest/meta-data/ with the updated code, which correctly returned an "access to cloud metadata IP is forbidden" error. Also ran go test ./... to ensure no regressions were introduced.

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PR created automatically by Jules for task 3167999634774808332 started by @himattm

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