add markdown linting as a pre-commit hook

[ev-br]

Description

Add a pre-commit hook to lint markdown files in the docs/ folder, thus it will only run on files changed in a particular commit.
Linting all docs, via $ pre-commit run --all-files, generates a ~1kLOC patch, which is not including here. Can add it now if desired.

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[melissawm]

Looks good to me, thanks @ev-br !