docs(errors/large-page-data): how to see data being passed to page (#40491)
docs(errors/large-page-data): how to see data being passed to page (#40491)

## Summary

This PR adds a note about how to see the data that this error is complaining about:

```sh
Warning: data for page "/" is xxx which exceeds the threshold of 128 kB, this amount of data can reduce performance.
```

This debug trick was something I came across in a [discussion](https://github.com/vercel/next.js/discussions/39880) and I thought it would be helpful to others like it was for me.

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)


Co-authored-by: JJ Kasper <fbae0e752deb2c0fed663fa6dec6c97ee2546cfe@users.noreply.github.com>
JeromeFitz/next.js,JeromeFitz/next.js,JeromeFitz/next.js,JeromeFitz/next.js