Summary: Images in the network plugin are rarely displayed in the network plugin, as it tries to use the public url to preview it. However, that won't if the endpoint is behind authentication, idempotent, etc. This diff changes the behavior to instead send the network body to flipper and use that to preview. Changelog: [Network] Fixed image preview Reviewed By: jknoxville, passy Differential Revision: D23370743 fbshipit-source-id: 0070e9e38c10a5761b9f7190467e26f01a7b2471