add proxy_ignore_client_abort flag to Nginx conf

The `proxy_ignore_client_abort` flag specifies whether nginx will
monitor possible connection close while waiting for an upstream
server response. If an error occurs while sending a response, the
connection will be closed regardless of the flag, much like if
there were no nginx at all.

fixes #3484

support/nginx/peertube

@@ -154,6 +154,7 @@ server {
   keepalive_timeout         10s; # default is 75
   resolver_timeout          10s; # default is 30
   reset_timedout_connection on;
+  proxy_ignore_client_abort on;
 
   tcp_nopush                on; # send headers in one piece
   tcp_nodelay               on; # don't buffer data sent, good for small data bursts in real time