Update getServerSideProps docs with req.cookie note (#29457)
Update getServerSideProps docs with req.cookie note (#29457)



## Documentation / Examples

Add a note to the `getServerSideProps` docs that `context.req` [contains](https://github.com/vercel/next.js/blob/c27e3a41dcf9590fb1c9ba9b9e16517cf4cb49b4/packages/next/types/index.d.ts#L148-L150) a `context.req.cookies` attribute.

I based the copy off of the one from https://nextjs.org/docs/api-routes/api-middlewares.

Checklist:
- [x] Make sure the linting passes

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