Support configuration of scrape-interval + export-interval in prometheus-to-sd-kube-state-metrics.yaml

According to the Readme, prometheus-to-sd supports scrape-interval and export-interval params to configure the rate of scraping and exporting.
https://github.com/GoogleCloudPlatform/k8s-stackdriver/tree/master/prometheus-to-sd#scrape-interval-vs-export-interval

However the helm chart does not support configuring those values:
https://github.com/GoogleCloudPlatform/k8s-stackdriver/blob/master/prometheus-to-sd/kubernetes/prometheus-to-sd-kube-state-metrics.yaml#L32

We can work around this by forking the yaml but it would be a nice to have if the official version could support this :)