*Official form handling with file uploads example with Nitro + best practices

[franklin-tina]

It will be nice to an official repo/example that handles FormData with support for file upload, that can be used for reference when dealing with forms.

I recently ran into a situation when trying to save form data with a file, and I see a similar concern was raised in an old nuxt discussion.

There was a comment on another old nitro issue regarding h3's readMultipartFormData, but the result of using that helper wasn't as expected.

I feel this is an issue/blocker a lot of people have and I think it will be super cool to have some official docs or examples around the topic.

Thanks.
cc @pi0