[RFE] Support importing configuration regardless the status of the k8s control plan

[blanquicet]

Currently, we only support retrieving the nodes' information if the k8s control plan is working correctly because we use the API server. However, it is possible to use the Azure API and avoid passing through the API server so that we can improve UX by allowing users to get such information in all the cases with kubectl-aks and they don't need to go to the portal or use az.

Here the way to do it using az, we need to find the corresponding APIs to reproduce the same programatically:

Infrastructure/Node resource group: Using the cluster name and resource group, we can retrieve the infrastructure/node resource group like this:

$ az account set --subscription <subscription-id> 
$ az aks show --name <cluster-name> --resource-group <resource-name> --query nodeResourceGroup 
"MC_my-rg_my-cluster_my-location" 

VMSS: Using the infrastructure/node resource group name we can retrieve the VMSS:

$ az resource list --resource-group MC_my-rg_my-cluster_my-location --resource-type Microsoft.Compute/virtualMachineScaleSets --query [].name 
[ 
  "aks-agentpool-12345678-vmss" 
] 

VMSS Instance ID: And using the VMSS we can get the mapping between instances ID and nodes:

$ az vmss list-instances --resource-group MC_my-rg_my-cluster_my-location --name aks-agentpool-12345678-vmss --query "[].{VMSSInstanceID: instanceId, NodeName: osProfile.computerName}" -o table 
VMSSInstanceID    NodeName 
----------------  --------------------------------- 
0                 aks-agentpool-12345678-vmss000000 
1                 aks-agentpool-12345678-vmss000001 
2                 aks-agentpool-12345678-vmss000002