Use cluster-proportional-autoscaler as dependency

[hagaibarel]

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

[shubham-cmyk]

@hagaibarel Assign this to me