Please support configuring environment variables for the cluster-proportional-autoscaler container

E.g. to enable configuring Go runtime with GOMAXPROCS and GOMEMLIMITS environment variables.

Optionally, consider setting GOMAXPROCS and GOMEMLIMITS env vars automatically relative to the configured resources (CPU requests, and memory limits, respectively), when resources are configured.

With current default resource configuration (20m CPU requests and limits) and no GOMAXPROCS configured, there's lots of CPU throttling. Upstream chart doesn't set default resource configuration, so partially issue could be solved with https://github.com/coredns/helm/issues/103 - at least it would move upstream.