Add workflow to deploy docs preview on PR

[rly]

Is your feature request related to a problem? Please describe.

It would be nice to preview how a change to the docs looks without having to build the docs locally. You can do this using https://github.com/rossjrw/pr-preview-action. The NWB team uses it for their github pages page - example workflow here https://github.com/NeurodataWithoutBorders/nwb_hackathons/blob/main/.github/workflows/test-pages-build.yml

I think it will run on every PR, and since most PRs don't change the docs here, this is probably unnecessary. I would configure this to run only if something in the docs folder has been changed.

How important is this feature?
• Low - it's an enhancement but not crucial for work

When will use cases depending on this become relevant?
• Long-term - 6 months - 1 year