Next.js code on React auth page

**Describe the content issue**:
There is incorrect content on the https://docs.amplify.aws/react/build-a-backend/auth/set-up-auth/ page. The pages/_app.tsx referenced doesn't normally exist in a React app, the "pages" dir and the code snippet for it seem to be for next.js app. They use "pages" dir in older versions, and one of the imports is from 'next/app'.

Also, I did a manual install in an existing React app. The "npm add @aws-amplify/ui-react" failed, after doing the "npm add --save-dev @aws-amplify/backend@latest @aws-amplify/backend-cli@latest typescript" initially. Because one of the ui-react dependencies wanted to use a lower version of typescript then was installed at the beginning.

**URL page where content issue is**:
https://docs.amplify.aws/react/build-a-backend/auth/set-up-auth/