feat: renamed PRIMARY_HOSTNAME to BOX_HOSTNAME

using "primary" to describe the domain of the box / mail server is confusing when working with multiple domains.
Usually the box domain is different from the domain you want to host your mail for.

conf/zpush/autodiscover_config.php

@@ -10,7 +10,7 @@ define('TIMEZONE', '');
 // Defines the base path on the server
 define('BASE_PATH', dirname($_SERVER['SCRIPT_FILENAME']). '/');
 
-define('ZPUSH_HOST', 'PRIMARY_HOSTNAME');
+define('ZPUSH_HOST', 'BOX_HOSTNAME');
 
 define('USE_FULLEMAIL_FOR_LOGIN', true);