docs: Refactor `next` and `create-next-app` CLI pages (#68899)
Closes: https://linear.app/vercel/issue/DOC-3249/cli-reference-pages
Updates the `next` and `create-next-app` CLI pages to follow the
reference page template. Moves these pages under "CLI" to match new IA.
Redirects: https://github.com/vercel/next.js/pull/68899
