Configure cache settings for Nginx

Cache expires after 24h.
After cache is expired, browser can compare ETag to the server to check if the file has changed. If the server returns the same token, then the file is the same, and there's no need to re-download it.

(cherry picked from commit b511f2094f6961bd6d353b86cf8d0d065536d04f)

server/nginx.conf

@@ -22,6 +22,8 @@ http {
     #tcp_nopush     on;
 
     keepalive_timeout  65;
+    expires 86400;
+    etag on;
 
     include /etc/nginx/conf.d/*.conf;