add forward_auth to redirect parameters from source to target with push

[younes200]

Add forward_auth to allow push stream with attached authentification.

Example :

worker_processes auto;
rtmp_auto_push on;
rtmp_auto_push_reconnect 1s;
events {}
rtmp {
    server {
        listen 1935;
        listen [::]:1935 ipv6only=on;
        chunk_size 4096;

        application live {
            live on;
            record off;
            push rtmp://127.0.0.1:19350/live;
            forward_auth on;
        }
        
    }
}

Related issue #920