DEV/CI: docs build previews

[lucascolley]

It would be convenient to have the docs build artefacts produced by https://github.com/data-apis/array-api-extra/blob/main/.github/workflows/docs-build.yml on PRs hosted somewhere, so that one doesn't have to download the files and preview them locally.

[lucascolley]

@rgommers would it be annoying from an infrastructure perspective to setup CircleCI for this repo?

This isn't high priority, but it would be nice for DX to have docs previews, so I'm trying to figure out what the best way to get that would be.

[rgommers]

Eh, maybe - the current Circle preview action has an issue, it requires too many permissions and doesn't work now that we tightened those up on the scipy repo: scipy/scipy#23007. I'd like to let that run its course first before doing anything here.