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.

Fix issue that PHP version of a site gets altered when an admin edits the site when domain limit mode is active.

add documentation and example for mail_relay_domain_delete function #6399