Add more pull request tests to enforce standards and quality

[jbampton]

There are a number of tools that can be setup to run basic checks or tests.

Listing here some improvements we could add:

• link checkers: lychee or markdown-link-check
• spell checkers: codespell or typos
• linters: markdownlint, yamllint, actionlint, zizmor, shellcheck, ruff, oxipng, bandit and more...
• pre-commit which can run both locally and with actions on GitHub

[sebbASF]

It also would be useful to know when links are lost, e.g. an anchor is renamed without a replacement alias, or a page moved without a redirect.