Chore: change Next.js build output folder

[nickytonline]

Following #4094 and #4096, we might want to consider a different build output folder for Next.js, like build instead of the default, .next and revert the changes in #4096.

I didn't do this in #4096 in case it caused other issues in the CI/CD pipeline. I think it should be fine, but just need to confirm on the Netlify deploy side of things.

[github-actions]

Thanks for the issue, our team will look into it as soon as possible! If you would like to work on this issue, please wait for us to decide if it's ready. The issue will be ready to work on once we remove the "needs triage" label.

To claim an issue that does not have the "needs triage" label, please leave a comment that says ".take". If you have any questions, please comment on this issue.

For full info on how to contribute, please check out our contributors guide.