[Feature] Support managed routetable for CNI Overlay for non-AKS usage

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Kubenet is being deprecated. For VM outside AKS subnet but within same VNet, we need another routetable to route VMs to access Pods in AKS.

I have checked this with ACI in different subnet, and this solution does work: The only thing need is to have this routetable being managed - so there is no need to modify routetable every time when node number is changed.







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CNI Overlay can generate a managed routetable for user to use: access Pod in AKS from non-AKS subnet.