Configure lint and formatter for markdown files

[notrab]

Since moving to Biome we haven't really had anyting in place for formatting .md, .mdx files.

We should standardise formatting as docs are now updated by many folks, there's PRs with larger diffs than necessary because of formatters being different for us.

Investigate best path. Biome to my knowledge doesn't have a markdown formatting option, so we could introduce a plugin (if such exists for Biome), Prettier, or something more bespoke like a markdown format package only.

This should be added and checked in the same way Biome does its checks. We should not merge anything that is not formatted, or contains linting issues (e.g. prefer - instead of * for lists).

[lightwalker-eth]

@notrab Thanks for logging this opportunity 👍 I believe @Y3drk has worked on a similar opportunity in ENSAwards where if I remember correctly, multiple linters / formatters are configured to work in parallel for similar reasons. Perhaps you could both discuss this opportunity and decide on the best path forward? Thanks!

[notrab]

@lightwalker-eth @Y3drk I can PR this tomorrow and match the ENSAwards implementation for consistency 👍🏻