Azure vm_size options have changed

[johnson-m-d]

gitops-foundations-env-2892009/terraform/aks-k8s-cluster.tf

Line 32 in 5044d29

vm_size = "Standard_D2_v2"

This line results in an error which returns a wide array of valid options. For my follow along, I picked "standard_d2s_v3". Azure suggests this line won't be needed soon, but as of now it still is.