Swap from superlinter to a markdown-specific linter

[alice-i-cecile]

What problem does this solve or what need does it fill?

superlinter handles a ton of different languages. We don't need that, and swapping to a simpler, purpose-built tool would reduce churn (e.g. #18320) and may improve performance.

What solution would you like?

https://github.com/akiomik/mado is written in Rust (so we can easily help maintain it), and is advertised as being much faster.

What alternative(s) have you considered?

Find some other markdown linter.

#8471 tried this with markdownlint-cli2-action, which stalled out.

Additional context

The mado author's Github profile lists them as a bird lover.

[mockersf]

very opposed to switch from markdownlint to something that new