Add maintenance page feature to Mastodon nginx site

site-cookbooks/kosmos-mastodon/templates/default/nginx_conf_mastodon.erb

@@ -35,6 +35,11 @@ server {
   add_header Strict-Transport-Security "max-age=31536000";
 
   location / {
+    # If the maintenance file is present, show maintenance page
+    if (-f <%= @mastodon_path %>/public/maintenance.html) {
+      return 503;
+    }
+
     try_files $uri @proxy;
   }