ci: add netlify preview

[dshemetov]

Checklist

Please:

• Make sure this PR is against "dev", not "main" (unless this is a release
  PR).
• Request a review from one of the current main reviewers:
  brookslogan, nmdefries.
• Makes sure to bump the version number in DESCRIPTION. Always increment
  the patch version number (the third number), unless you are making a
  release PR from dev to main, in which case increment the minor version
  number (the second number).
• Describe changes made in NEWS.md, making sure breaking changes
  (backwards-incompatible changes to the documented interface) are noted.
  Collect the changes under the next release number (e.g. if you are on
  1.7.2, then write your changes under the 1.8 heading).
• See DEVELOPMENT.md for more information on the development
  process.

Change explanations for reviewer

This adds the docs preview command: /preview-docs to this package.

Magic GitHub syntax to mark associated Issue(s) as resolved when this is merged into the default branch

• Resolves #{issue number}

[brookslogan]

This looks really cool.

Workflow file looks probably good as far as I can tell, but I'm not too familiar with GitHub Actions and don't know Netlify. I tried to limit my questions down below but you can skip answering if you'd like, or alternatively, put answers/reminders in comments in the workflow file.

One question below not to skip is about whether this could potentially clobber anything valuable on Netlify. I don't know how to check that so maybe you could double-check somehow?

---

suggestion: add a mention of how to trigger this in DEVELOPMENT.md or the pull request template?

[dshemetov]

Thanks for looking into this! I

• reduced the CI permissions
• removed the extra PR_NUM step
• added lots of comments for all the options

As for the clobbering question: the Netlify sites all have separate SITE_ID which points to different sites on my Netlify account, so there won't be clobbering.