feat(dev-server): redirect requsts without base url

[danielroe]

🔗 Linked issue

resolves nuxt/cli#469

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 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 is a quality-of-life improvement rather than a bugfix per se.

If a baseURL is provided, this means that we can redirect user to it if they access a different URL.

📝 Checklist

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