Do not strip Cache-Control headers from media. Trust the Pleroma backend.

installation/pleroma.nginx

@@ -90,8 +90,6 @@ server {
         proxy_ignore_client_abort on;
         proxy_buffering    on;
         chunked_transfer_encoding on;
-        proxy_ignore_headers Cache-Control;
-        proxy_hide_header  Cache-Control;
         proxy_pass         http://127.0.0.1:4000;
     }
 }