chore: add markdown linter

[Elia-Renzoni]

This PR adds a make target for running Markdown lint checks with the following features:

• Checks for markdownlint-cli: If is not installed, it will automatically install it.
• Requires NPM: If NPM is not available, the target fails immediately.
• Targetable directories: By default, it lints the docs/ folder, but a custom target can be specified. Example: make markdown-lint target=./README.md
• Auto-correction: It can automatically fix issues. Optionally, we could split this into two targets, one for checking only, and one for fixing.

Related Issue: #4000

[ngjaying]

LGTM. The addition of a local markdown-lint target is helpful for development parity with CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.80%. Comparing base (5dee73c) to head (7d4fcb2).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4004      +/-   ##
==========================================
- Coverage   71.87%   71.80%   -0.08%     
==========================================
  Files         460      460              
  Lines       53183    53183              
==========================================
- Hits        38224    38184      -40     
- Misses      12024    12052      +28     
- Partials     2935     2947      +12     

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