feat: Ability to disable default MDX plugins

[felixsanz]

What is it?

• [x] Feature / enhancement
• [ ] Bug
• [x] Docs / tests

Description

This PR let the developer disable some MDX plugins that were included by default with qwik-city (only the optional ones and it's opt-in, by default they are enabled like before).

This plugins are remarkGfm, rehypeSyntaxHighlight and rehypeAutolinkHeadings.

It is really useful because when those plugins are disabled, the developer can now pass the same plugins to MDX with a different configuration. Right now it's impossible to re-configure rehypeAutolinkHeadings or to use another syntax hightlighter, for example.

Fixes https://github.com/BuilderIO/qwik/issues/1021.

Use cases and why

• 1. One use case
• 2. Another use case

Checklist:

• [x] My code follows the developer guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] Added new tests to cover the fix / functionality

[felixsanz]

@shairez This is #1177. I needed to re-create the PR because of a git mess

[shairez]

Thanks so much @felixsanz !

Summoning the all knowing @adamdbradley to take a second look to verify that everything looks good

[jrson83]

Would be awesome if merged.

[manucorporat]

lets get this merged soon!

[manucorporat]

I will look into all this next week!