Add working code blocks

[roadlittledawn]

Summary

Add ability to have live preview of code in code block.

Outstanding Qs

• how would this work for node?

Acceptance criteria

• [ ]

Helpful links

• https://github.com/newrelic/gatsby-theme-newrelic/blob/develop/packages/gatsby-theme-newrelic/src/components/CodeBlock.js
• https://developer.newrelic.com/components/area-chart

[roadlittledawn]

could maybe use codesandbox dev box embeds for backend code

for frontend could use jsfiddle / codesandbox / codepen embeds