Add nodeSelector support to charts

[tillig]

With an AKS cluster that has both Windows and Linux nodes in it, you need to be able to specify a nodeSelector:

  nodeSelector:
    beta.kubernetes.io/os: linux

Without that, Linux deployments get scheduled on Windows nodes and none of the examples ever actually work.

Even if that's not set up as default, the ability to provide that in a values.yaml or --set call from Helm would be huge. In our mixed cluster, I can't use any of these Helm charts.