Draft: Markdown PoC

What does this MR do and why?

Proof of Concepts: Try out different CommonMark parsers, based on Update markdown parsing/rendering on the backen... (&10074)

• https://github.com/jgm/commonmark-hs, a Haskell version
• https://github.com/kivikakk/comrak, Rust version driven by the latest version of https://github.com/gjtorikian/commonmarker
• https://github.com/rlidwka/markdown-it.rs, Rust version driven by https://gitlab.com/digitalmoksha/glfm_markdown

Currently using gitlab-glfm-markdown