install/tpl/gentoo_postfix.conf.master
updated based on debian config

added <IfModule mod_version.c> because gentoo has no mod version installed by default
added <IfModule mod_proxy_fcgi.c>

install/dist/lib/gentoo.lib.php
updated functions:
configure_postfix
configure_dovecot
install_ispconfig

added configuration for pureftpd versions greater than 1.0.50

added function get_host_ips() because gentoo does not provide IPs with "hostname --all-ip-addresses"

Use central predefined 4096 bit DH params file (from Mozilla https://ssl-config.mozilla.org/ffdhe4096.txt ) instead of creation one via openssl command to speed up the installation. Thank you to @ahrasis for code suggestions.

Rename Mailman data directory if it exists and Mailman is not installed to prevent broken routes (#6314)