Add syntax highlighting to JSON views (request preview and response)

[apreifsteck]

Did you search for existing issues already?
Yes 👍

Is your feature request related to a problem? Please describe.
No, just a qol improvement

Describe the solution you'd like
Syntax highlighting for json bodies in request and response views

Describe alternatives you've considered
N/A

Additional context
Httpie for desktop has a very pretty interface that I think could port well to Slumber. That's what inspired this feature request.