php, move session files into it's own directory

src/etc/inc/plugins.inc.d/webgui.inc

@@ -68,6 +68,7 @@ function webgui_configure_do($verbose = false, $interface = '')
     }
 
     chdir('/usr/local/www');
+    @mkdir('/var/lib/php/sessions', 0750, true);
 
     /* defaults */
     $portarg = '80';

src/opnsense/service/templates/OPNsense/WebGui/php.ini

@@ -25,3 +25,4 @@ display_errors=on
 log_errors=on
 error_log=/tmp/PHP_errors.log
 date.timezone="{{system.timezone|default('Etc/UTC')}}"
+session.save_path=/var/lib/php/sessions