fix: allow users to override nitro error

[danielroe]

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 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)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Previously it was impossible to override sub-paths (for example, #nitro/error) as #nitro was added first to the alias object.

Do not yet merge as there is an error that this reveals in Nuxt that needs to be resolved first: resolved in nuxt/framework#4215

📝 Checklist

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

[pi0]

We might use #nitro-* alias for a temporary error alias workaround. I don't think reusing #nitro namespace is best idea in terms of stability.