Report doc preview status in PRs

[jprochazk]

What

This is part 1 of documentation preview improvements.

• Add ability to wait for deployment to .github/actions/vercel
• Report current status in the PR comment
• Test all failure paths

Output examples

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

To run all checks from main, comment on the PR with @rerun-bot full-check.

[github-actions]

Latest documentation preview deployed successfully.

Result	Commit	Link
✅	7ca5cbb	https://landing-62kdd1rre-rerun.vercel.app/docs

^{Note: This comment is updated whenever you push a commit.}