fix(proxy): better error when upstream proxy fails

[TheAlexLichter]

🔗 Linked issue

#722

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• [x] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [x] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR should ensure that proxyRequests fail gracefully instead of leading to an unhandled node error crashing the server.

📝 Checklist

• [x] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.