Create a better `<Code>` component

[Josh de Leeuw]

The admin/[experiment_id].js page has a feature to show the code necessary to communicate with the server. I used Chakra's basic <Code> component, but it lacks a lot of features that would be nice to have, like syntax highlighting and a copy to clipboard button. It's also difficult to get the formatting right. Let's figure out a way to fix this...