Suggestion: Update useGetStaticProps to support Next.JS v10 notfound

Next.JS now supports returning 404 responses when fallback is true using a new property.

It would be great if support for this could be added to the next-slicezone package's useGetStaticProps hook to allow it to return a 404 if pages aren't available when fallback is enabled.

This is a great idea, can you add this as an RFC on the slice-machine Github? That way we can start the conversation with the team.