Improve the Scale-In functionality of Set-AksHciCluster

Sometimes, you may need to explicitly specify which k8s worker nodes you want to kill while scaling in. Perhaps you have FCM/S2D issues or maybe there's just something wrong with a VM and you don't want to waste time triaging (cattle, not pets).

Currently, `Set-AksHciCluster` only allows you to specify a count of worker nodes. Presumably there are built-in smarts that pick the best candidate nodes to decommission when you opt to scale-in. It would be awesome to have a new parameter that let you specify the worker nodes to kill (k8s hostname, FCM resource name, whatever). I imagine it would be something like this:

Assuming there are currently 7 Linux Worker Nodes and you want to reduce down to 5

`Set-AksHciCluster -linuxNodeCount 5 -linuxNodesToScaleIn @('k8s-cluster-default-linux-nodepool-md-nr9dx-8b48eab5', 'k8s-cluster-default-linux-nodepool-md-kth4x-1db964b8')`

The logic during the scale-in would check if `NewNodeCount == (OldNodeCount - HostnameCollection.Length)` to make sure you aren't specifying too many node names.