chore: lint doc with markdownlint

What does this merge request do and why?

This MR adds markdownlint-cli2 tool to lint documentation in markdown. The configs are copied from GitLab project.

I have removed the custom rules since they require node to be set up (we use mise to manage markdownlint-cli2 binary). Additionally, these rules are tabs-related and are not applied for this repository.

How to set up and validate locally

1. Check out to this merge request's branch.
2. Install markdowlint-cli2 binary.

   mise install

3. Run doc linting.

   $ make lint-doc
   Running vale...
   ✔ 0 errors, 0 warnings and 0 suggestions in 13 files.
   Running markdownlint...
   markdownlint-cli2 v0.13.0 (markdownlint v0.34.0)
   Finding: docs/**/*.md README.md
   Linting: 13 file(s)
   Summary: 0 error(s)

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.