Add UI to display network request/response body

[ryan953]

This should be feature flagged to Sentry internal only.

Build the figma: https://www.figma.com/file/SVyNvm8p17xGfIC7r7l2YS/Specs%3A-Network-Request-Details?node-id=0-1&t=txyAFdHK7PGHYQGK-0