🛡️ Sentinel: [CRITICAL] Fix SSRF vulnerability in plugin fetcher

[mttmcknn]

🚨 Severity: CRITICAL
💡 Vulnerability: http.Get() was used directly for fetching plugins from user-supplied URLs without mitigating SSRF targeting cloud metadata IP (169.254.169.254).
🎯 Impact: An attacker could coerce the application to fetch sensitive metadata from cloud environments via SSRF.
🔧 Fix: Created and utilized a custom http.Client with a net.Dialer control hook that strictly blocks access to the 169.254.169.254 metadata IP during DNS resolution before the socket connects. Explicitly disabled keep-alives and configured timeouts to prevent resource exhaustion.
✅ Verification: Verified that go test ./... passes and go build ./... compiles successfully.

---

PR created automatically by Jules for task 13606388046376229231 started by @himattm

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.