Enable Marketplace for Flipper (#3491)

Summary:
This is PR on top of: https://github.com/facebook/flipper/pull/3473

It adds an option to Settings to allow distribution of marketplace plugins.

Also includes a simple fetch function to retrieve data from external API/server.

## Changelog

Allow marketplace plugins

Pull Request resolved: https://github.com/facebook/flipper/pull/3491

Test Plan:
1. Enable marketplace
2. Provide custom marketplace server (it will serve the list of internal plugins with downloadURL)
3. Test if can see Available plugins and can download/remove the plugin
4. If new update for the plugin, it should also allow auto update

Reviewed By: antonk52

Differential Revision: D34586339

Pulled By: nikoant

fbshipit-source-id: c887982aa0f0f9abd3b5360f22e8692a2445d345

desktop/scripts/jest-setup-after.tsx

@@ -150,6 +150,9 @@ function createStubRenderHost(): RenderHost {
       },
       showWelcomeAtStartup: false,
       suppressPluginErrors: false,
+      enablePluginMarketplace: false,
+      marketplaceURL: '',
+      enablePluginMarketplaceAutoUpdate: true,
     },
     validWebSocketOrigins: [],
   };