How can I do ratio based or percentage based routing in Apigee as provided in Zuul and istio

[#1]

I need to create a service proxy which will route the traffic based on some conditions and configurations.

for example service calls which have header {clientId : XXXX} should be routed 95% to legacy service and 5% to new service.

This feature is available in Zuul and Istio. How we can implement the same in Apigee