prometheus.yaml and servicegraph.yaml is missing in istio master branch.
However, the document still ask customers to use, as below
In https://istio.io/docs/tasks/telemetry/querying-metrics.html, use command
kubectl apply -f install/kubernetes/addons/prometheus.yaml

In https://istio.io/docs/tasks/telemetry/servicegraph.html, use command
kubectl apply -f install/kubernetes/addons/servicegraph.yaml