The SystemAssigned managed identity requires a preview feature to be
enabled.
```
rgil@rem5:~/atst/terraform/providers/dev$ az feature list|grep MSIPreview
"id": "/subscriptions/95934d54-980d-47cc-9bce-3a96bf9a2d1b/providers/Microsoft.Features/providers/Microsoft.ContainerService/features/MSIPreview",
"name": "Microsoft.ContainerService/MSIPreview",
rgil@rem5:~/atst/terraform/providers/dev$ az feature register --namespace Microsoft.ContainerService --name MSIPreview
Once the feature 'MSIPreview' is registered, invoking 'az provider register -n Microsoft.ContainerService' is required to get the change propagated
{
"id": "/subscriptions/95934d54-980d-47cc-9bce-3a96bf9a2d1b/providers/Microsoft.Features/providers/Microsoft.ContainerService/features/MSIPreview",
"name": "Microsoft.ContainerService/MSIPreview",
"properties": {
"state": "Registering"
},
"type": "Microsoft.Features/providers/features"
}
rgil@rem5:~/atst/terraform/providers/dev$ az provider register -n Microsoft.ContainerService
rgil@rem5:~/atst/terraform/providers/dev$
```
This also now integrates the policy for keyvault with the k8s managed
identity (system assigned).
Specifying the node count breaks the autoscaling min/max. When this
happens, the k8s cluster needs to be manually reconfigured. Terraform
does not remove the node count even when the node count option is
removed. The k8s cluster resource needed to be destroyed and re-created
in order to resolve the issue with node count and min/max options being
specified at the same time.
