Disallow robots from scanning metabase site (#11862)

Related to issue https://github.com/metabase/metabase/issues/2808

resources/frontend_client/index_template.html

@@ -4,6 +4,7 @@
     <meta charset="utf-8" />
     <meta http-equiv="X-UA-Compatible" content="IE=edge" />
     <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no, minimal-ui" />
+    <meta name="robots" content="noindex" />
     <meta name="apple-mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
     <link rel="apple-touch-icon" sizes="180x180" href="/app/assets/img/apple-touch-icon.png">