404 checking in pipeline

[jsntn]

reference

• https://github.com/marccampbell/hugo-linkcheck-action
• https://github.com/marketplace/actions/404-links (via https://medium.com/@Olivierodo/markdown-link-checker-oh-my-github-action-1-edc31b7762d0)

[jsntn]

• https://github.com/marketplace/actions/broken-links-crawler