Make all Markdown plugins optional

[Barbapapazes]

Is your feature request related to a problem? Please describe.

Hello,

When building a custom theme, having the ability to disable as much Markdown plugins as possible could be very useful to ensure that VitePress can be highly customizable. Technically, it's not a breaking change but because the v2 is coming, I could be a good move to use this release to change this.

Happy to start a PR if needed.

Describe the solution you'd like

More options.

Describe alternatives you've considered

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the docs.
• Read the Contributing Guidelines.
• Check that there isn't already an issue that asks for the same feature to avoid creating a duplicate.

[brc-dd]

It's planned. Most likely similar to vuepress v2.