Update installer_base.lib.php to fix the missed svr_ip that should have been modified to include both ipv4 and ipv6 in the previous quick fix before 911 ispconfig/ispconfig3!911 proposal was merged.

This caused failure to create LE SSL certs as reported in issue 5731 ispconfig/ispconfig3#5731.

This commit is aimed to fixed the said issue.

Hj Ahmad Rasyid Hj Ismail authored Sep 08, 2020 and Till Brehm committed Sep 08, 2020

Update installer_base.lib.php to get LE SSL certs for the server via certbot or acme.sh before openssl self-signed method upon new installation or existing update; and extend it to other available services (postfix, pure-ftpd-mysql), with additional dhparam pem file, if none exists.

add postfix version check

add stress adaptive behavior (syntax changes with postfix version 3.0)

add smtpd_relay_restrictions (postfix version 2.10)