Allow users to specify a node pool VM to delete (with or without scaling)

**Title**:
Allow users to specify a node pool VM to delete (with or without scaling)

**Description**:
In simple terms, it would be slick to provide the logic to target a specific VM to kill; whether independently or when scaling down a node pool.

For scaling, perhaps add a new parameter only validates and works if the `-count` parameter is less-than current count. Something like `-targetVM` or `-targetNode`

As an example, let's say you have the following:
- **AKS Cluster Name**: k8scluster01
- **Pool Name**: k8scluster01linuxpool01

And in that pool, you have 3 nodes with VM names:
- k8scluster01linuxpool01-AAAAAAA
- k8scluster01linuxpool01-BBBBBBBB
- k8scluster01linuxpool01-CCCCCCC

And assume that `k8scluster01linuxpool01-CCCCCCC` has some kind of failure that has to be manually fixed by simply deleting the entire VM from the cluster.

If we had the ability to run `Set-AksHciNodePool -clusterName "k8scluster01" -name "k8scluster01linuxpool01" -count 2 -targetNode "k8scluster01linuxpool01-CCCCCCC"` , it would be smart enough to see that `-count 2` is less than current value and we are targeting a specific VM to remove.

For non-scaling situations where you just want to kill a VM and have it respawn, make a new cmdlet called `Remove-AksHciNodePoolVM` or `Remove-AksHciNodePoolNode` that handles this logic.