Add github action that builds on a PR and pushes to staging site for rendering

[yarikoptic]

I believe this is the wishlist request with github on having such a feature for gh-pages: https://github.com/github/feedback/discussions/7730 which points to workarounds like https://github.com/blueedgetechno/win11React/blob/master/.github/workflows/gen-preview.yml .

In principle, it should be possible to

• create datalad.org-previews/ organization
• per each new PR create a new fork there (e.g. datalad.org-pr108) with gh-pages enabled
• use ideas from aforementioned workflow to orchestrate it all and announce preview URL to the PR
• master workflow would remove "preview" repositories for merged PRs

Sounds like a good idea for a parametrized github action, so there might be one by someone already -- worth doing a bit more googling.

[jsheunis]

Look into netlify: https://www.netlify.com/pricing/?utm_medium=paid_search&utm_source=google&utm_campaign=12755510784&utm_term=netlify