docs: add description of returning different status codes

[MikeBellika]

❓ 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

Add description of how to use createError and event.node.res.statusCode from server directory.
There is already documentation of createError on https://nuxt.com/docs/api/utils/create-error#throwing-errors-in-api-routes. However I think this is a common enough use case, that it should be documented directly on https://nuxt.com/docs/guide/directory-structure/server.

For documentation of how to use non error status code, I couldn't find anything in the docs for server routes. I found https://nuxt.com/docs/api/utils/set-response-status, however this doesn't seem to work for server routes.

As a personal anecdote, I had to implement different status codes. I expected to find a guide in the server routes documentation, but I had to do some more searching. To set non error status codes I had to look in the h3 docs.

📝 Checklist

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

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