Default value of wait_timeout should be the same as in MariaDB

The default value of wait_timeout in MaxScale is zero which disables the feature. Due to the changes in the default values of readwritesplit for 24.02, it is now a lot more common to run into situations where the connections of an idle client are killed by the server but MaxScale leaves the idle client alive. By using the same default value in MaxScale that is used in MariaDB, idle clients would eventually be kicked out.