Add syntax highlighting imports if a markdown file contains code blocks with languages set

[paulbrimicombe]

🧐 What?

• Adds client-side syntax highlighting for code blocks in Markdown files
• This will automatically add syntax highlighting to all relevant pages without the need for client opt-ins

🛠 How

• If a page has one or more code blocks with a language, import tags are added for HighlightJS (these are managed in / provided by morty)

👀 See