[Feature suggestion] Integrate Markdown support

[compwizard310]

The rich text editor in objects like knowledge base entries et similia is not very versatile and controllable for me. Most of the times it feels like I'm fighting against it. Embedding code blocks isn't comfortable and writing docs isn't as easy as it would be if it just was Markdown. With Markdown it would be very easy to write actual documentation. I'd prefer to be able to use GLPI for docs instead of having to rely on other tools like docusaurus or mkdocs, and a Markdown integration would be a significant first step towards this solution. Otherwise some way to integrate with other Wiki-like docs system would be appreciated.