Move DetailSidebar to flipper-plugin

Summary: This moves `<DetailSidebar>` component to `flipper-plugin` and documents it. No semantic changes.

Reviewed By: passy

Differential Revision: D27234575

fbshipit-source-id: 74640602d718f84ad999f5dac0420089796ed7fb

desktop/flipper-plugin/src/index.ts

@@ -56,6 +56,7 @@ export {
   createNuxManager as _createNuxManager,
 } from './ui/NUX';
 export {Sidebar as _Sidebar} from './ui/Sidebar';
+export {DetailSidebar} from './ui/DetailSidebar';
 
 export {renderReactRoot} from './utils/renderReactRoot';
 export {