Add MDX Support

[m-clare]

Is your feature request related to a problem? Please describe.
Feature request for added functionality (MDX support).

Describe the solution you'd like
I'm currently using a fork of this project that I've modified to include MDX support, and I wanted to know if this is something that would be of interest as part of the main repo.

Additional context
I'm holding off on doing anything more until the main branch of Gatsby upgrades to MDX v2 to try and pass all the tests for this project (currently my fork has some issues with package versioning).

[alxshelepenok]

Hi, there are no plans to implement integration with mdx yet, so for now, I will close the issue.