Add Markdown CI GitHub Actions

[benbhall]

Check docs markdown on PR for the following:

• Insensitive, inconsiderate writing (Alex.js)
• Markdown style rules.
• Broken links and images (https://github.com/restqa/404-links)

All of the tools used are configurable further in the yml or through additional config files. We'll probably need to do a bit of rule tweaking through these routes.

Triggers for PRs where it will be visible to reviewers but we had better not add it to the branch policy until we get on top of existing errors and add any valid ignores.

Notes

• The only marketplace offerings for Alex.js are bots that put commit suggestions in PRs, which is just a pain really. So I am calling it directly as a Node script.
• markdownlint (https://github.com/markdownlint/markdownlint) is a well-established tool for markdown linting and there is a stable GitHub action wrapping markdownlint-cli that I have used.
• For broken link and image checking in markdown I prefer https://github.com/mike42/mdcheckr but it is getting old now so trialling one with a GitHub Action: https://github.com/restqa/404-links.
• 404 Links Action is also the flakiest as it is upset easily by sites not running https etc. Although to be fair, Chrome won't let me at those either e.g. https://ukho-design-system.jgwdns.co.uk/principles/delivery/testing.html#anchor3

[nevillejrbrown]

What is the output of the checks & where does it end up?

[benbhall]

What is the output of the checks & where does it end up?

They will surface as such:

Then following through to details you can find a breakdown of all errors under the 3 checks: