Narrow the opengraph-image function return type (#91893)
### What?
Change the `opengraph-image` return type to only `Response`.
### Why?
This function must return a `Response` object. The other documented
types cause Next.js builds to fail. I found this out the hard way by
following the documentation.
### How?
Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
