Feature: #65791 - Use PHP configured sendmail path, if [MAIL][transport] = sendmail is active

See forge#65791


The install tool setting [MAIL][transport_sendmail_command] is now retrieved automatically from PHP runtime configuration sendmail_path during installation (instead of '/usr/sbin/sendmail -bs').


There are no impacts on current installations.

New installations will have [MAIL][transport_sendmail_command] automatically set during installation using sendmail_path from PHP runtime configuration. It can still be changed manually.

As this setting is only used if [MAIL][transport] is set to sendmail, it doesn't have impact on other transport schemes.