FEAT: add `NGINX_IPV6` env to toggle nginx IPv6 listening

[yuuzukatsu]

Hello,

I've been running into some problem with the default configuration listening to IPv6. I was hoping with this env, it enables user to toggle whether they want to listen on IPv6 address or not

adding NGINX_IPV6=false environment will delete line containing listen [::]: on both /etc/nginx/site-opts.d/http.conf and /etc/nginx/site-opts.d/https.conf

I've tested this entrypoint script changes specifically in 8.2-fpm-nginx but adding few lines like this should work in most nginx variation

Thank you