feat: generate image metadata (#48362)
### What?
* Support `generateMetadata(props)` to dynamically generate multiple
metadata images at the same time
```js
// /app/opengraph-image.tsx
import { ImageResponse } from 'next/server';
export async function generateImageMetadata({params}) {
const images = await ...;
return images.map((img, idx) => ({
size: { width: 1200, height: 600 },
alt: img.text,
contentType: 'image/png',
id: idx,
}));
}
export default async function ({params, id}) {
const text = await getTextFor(id);
return new ImageResponse(
(
<div
style={{...}}>
{text}
</div>),
{ width: 1200, height: 600 },
);
}
```
### How?
Use `<metadata image>/[[...__metadata_id__]]/route.js` to catch all
metadata images id, and then use this `params.__metadata_id__` as id
argument for dynamic generate image.
If there's param, then we create `<metadata image>/<id>`, if there's
only 1 static image without dynamic `generateImageMetadata` then we keep
use `<metadata image>`
Closes NEXT-896
