perf(app-proxy): preconnect the media origin and revalidate the app shell (#1827)

fluxer_app/index.html

@@ -7,6 +7,8 @@
 <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover, interactive-widget=resizes-content, maximum-scale=1, user-scalable=no">
 <meta name="description" content="Fluxer is a free and open source instant messaging and VoIP chat app built for friends, groups, and communities.">
 <link rel="preconnect" href="{{STATIC_CDN_ENDPOINT}}">
+<link rel="preconnect" href="{{STATIC_CDN_ENDPOINT}}" crossorigin>
+<link rel="preconnect" href="{{MEDIA_ENDPOINT}}">
 <link rel="manifest" href="/manifest.json">
 <link rel="icon" type="image/png" sizes="32x32" href="{{STATIC_CDN_ENDPOINT}}/web/favicon-32x32.png">
 <link rel="apple-touch-icon" sizes="180x180" href="{{STATIC_CDN_ENDPOINT}}/web/apple-touch-icon.png">