Support for code blocks

We require code block support to use Featurebase. ProseMirror supports this and I see there is inline support and ``` support (albeit it's hidden and only works sometimes). This is for providing post content and replies with code examples. Ideally this needs syntax highlighting too.

Here is an example of what we currently have:

[https://fb-usercontent.fra1.cdn.digitaloceanspaces.com/1678813910545.png]

Thanks