add node example to open graph image docs (#64305)
### What?
Adds a Node.js example for using assets with `ImageResponse` to create
og images.
### Why?
The only examples available use `new URL` and `fetch` which does not
work when the runtime is using Node.js.
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Co-authored-by: Delba de Oliveira <32464864+delbaoliveira@users.noreply.github.com>
