Update next-intlayer reference in i18n doc (#83761)
[`next-intlayer`](https://intlayer.org/doc/environment/nextjs) is an
i18n library that adopts a per-component approach to manage multilingual
content in a next.js application.
### Changes
- Fix doc related to page-router documentation,
- And add App Router realted doc.
Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
