Add a mod_remoteip for sites behind reverse proxies like Cloudflare

Add option for setting users_apache_remote_ip_header: X-Forwarded-For to add:

RemoteIPHeader X-Forwarded-For

See:

• https://httpd.apache.org/docs/2.4/mod/mod_remoteip.html
• https://support.cloudflare.com/hc/en-us/articles/360029696071-Restoring-original-visitor-IPs-Option-2-Installing-mod-remoteip-with-Apache