Can we provide gke backend services urls as target endpoints in apigee proxy configuration?
Do you mean refer to Kubernetes service urls (..svc.cluster.local) from Apigee proxy ?? If so, no. K8s dont expose the service urls outside its cluster.
If you have K8s ingress service exposed via NodePort , you can refer it from Apigee by pointing to the IP address of the Instance and the Port (not recommended for Prod deployments). OR if you have a frontend loadbalancer fronting the K8s service, you can refer to the loadbalancer ingress ip (or fqdn pointing to the LB) from within Apigee proxy.
Thanks.