fix: Restore DNS prefetching for static resources (#1820)

* fix: Restore DNS prefetching for static resources

* fix: CDN paths
feat: preload instead of prefetch for key bundles

* csp

* fix: Turns out prefetch-src is still behind a flag in Chrome, not publicly available yet

server/static/index.html

@@ -4,6 +4,7 @@
     <title>Outline</title>
     <meta name="slack-app-id" content="//inject-slack-app-id//" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    //inject-prefetch//
     <link
       rel="shortcut icon"
       type="image/png"