Correct format for autoplay attribute in NextJS video docs (#62695)
### What?
Updates the format of the `autoplay` attribute in the [videos
documentation](https://nextjs.org/docs/app/building-your-application/optimizing/videos#common-video-tag-attributes)
to camel case, which is the correct format for the attribute in JSX,
matching the format of `playsInline`.
Co-authored-by: Sam Ko <sam@vercel.com>