Hi SushulKumar Yadav,
Thank you for responding for this article. This $clientIp keyword for the template has been released through an update for the WSO2 API Manager 2.6.0. Hence, you can try the scenario by using a WUM updated WSO API Manager 2.6.0 pack.
If the $clientIp keyword is available, you will able to see that when point to the question mark near to the Key Template field.