Add support for accepting the Proxy Protocol

[jkbys]

If set env as below:

ACCEPT_PROXY_PROTOCOL=true

"proxy_protocol" parameters are added to all listen directives in defaults.conf like as below:

listen 80 proxy_protocol;
listen 443 ssl http2 proxy_protocol;

Additinally, if set env as bellow:

ACCEPT_PROXY_PROTOCOL=true
SET_REAL_IP_FROM=172.16.0.0/12,192.168.0.0/16

"set_real_ip_from" and "real_ip_header" directives are added like as below:

set_real_ip_from 172.16.0.0/12;
set_real_ip_from 192.168.0.0/16;
real_ip_header proxy_protocol;

These lines are added to above of "log_format vhost" line, so the client IP address received from the proxy protocol is logged.