Allow node pool autoscaling opt out

[Dev25]

I would like to get a quick consensus before submitting the PR since there is a related prior issue: #83

We now use dynamic blocks quite a bit in this module, i would like to add a autoscaling bool flag (default is true) for node-pools to allow users to disable autoscaling on specific node pools if required.

This allows users to have whatever nodepool structure they want and the small benefit of not cluttering the autoscaling status (kubectl -n kube-system get cm cluster-autoscaler-status -oyaml) with nodepools that are fixed.

[morgante]

Thanks for checking in!

Now that this can be solved with conditional blocks, I'm on board with making autoscaling optional (but enabled by default).

We should still use min_count as the variable controlling the number of nodes, but the autoscaling flag would drop the autoscaling block and add node_count param.