feat(nuxt): allow remote sources for islands

[huang-julien]

🔗 Linked issue

resolve #12343
linked #19772

❓ 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

Hi 👋 (this pr has been sleeping for a while now...)

This should be considered as HIGHLY experimental

This PR opens the door to remote islands and introduce a new fallback slot for NuxtIslands which will show up if the component failed to fetch the island component

This feature can be enabled like this:

export default defineNuxtConfig({
  experimental: {
    componentIslands: 'local+remote'
  }
})

📝 Checklist

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

[huang-julien]

Tested with multiple tunnel locally. I wonder if its possible to test it within e2e fixtures