feat: markdown lint for docs

[kirillzyusko]

📜 Description

Added markdownlint to lint documentation markdown files.

💡 Motivation and Context

To improve consistency of markdown.

📢 Changelog

Docs

• align documentation to new linter standarts;

CI

• added job checking markdownlint;

🤔 How Has This Been Tested?

Tested locally (new docs) and on CI (markdownlint).

📝 Checklist

• CI successfully passed