Microsoft.ContainerService (AKS) count should not have a default value if autoscaling is set

[MacTynow]

When using AKS with Virtual Machine Scale Sets (VMSS) and the cluster-autoscaler (https://docs.microsoft.com/en-us/azure/aks/cluster-autoscaler), there shouldn't be a default for the count argument of agent node pools as seen hereunder. Since manual scaling is forbidden in that context this is causing issues when making changes to a cluster.

azure-rest-api-specs/specification/containerservice/resource-manager/Microsoft.ContainerService/stable/2019-08-01/managedClusters.json

Line 1349 in 4322d98

"default": 1

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @Azure/aks-pm.