Markdown Component - Greybox box

[bradystroud]

• [ ] New React Component if it doesn't currently exist
• [ ] Create a TinaCMS Block for this component
• [ ] Add block to Rule body.templates
• [ ] Update to support greybox conversion to React component
• [ ] Greybox appears in Rules/Rule

[Calinator444]

I converted the knowledge I gained from working on this PBI into a step in my Gatsby conversion documentation.

https://github.com/tinacms/tina.io/pull/2372/commits/5bdf4f0f1cd6205376d75b3dd15540a42b7ce5b2

[bradystroud]

Closing in favor of #1629