Add configuration for running Graphite (or some other statsd server) in Kubernetes

BuildGrid provides out-of-the-box support for monitoring with StatsD. Other solutions are possible but will require the development of extra tooling to ingest BuildGrid's metrics publishing.

We should get Graphite (or another statsd server, if that's easier/better) running in Kubernetes to use to monitor our BuildGrid cluster. We could do this with a helm chart, or by utilising some other existing solutions (an example), or by rolling our own configuration.