Use cluster-proportional-autoscaler as dependency

We currently use `cluster-proportional-autoscaler` by managing our own manifests and configuration. Since it's published as an independent chert, we can consume it as a chart dependency and offload the manifest management to ti, see the repo for more details - https://github.com/kubernetes-sigs/cluster-proportional-autoscaler

One thing to consider is that it will change the way values are passed from the `coredns` chart to the `cluster-proportional-autoscaler` one so it will be a major version change with a potential for breaking changes. We should also document the change and recommendations on how to migrate from version `1.x.x` -> `2.x.x`