[Feature] Dual Stack In Vnet pod ips

**Is your feature request related to a problem? Please describe.**
Some customers need their pod ips to be in vnet (for direct addressing inbound or outbound to rest of vnet). Azure cni podsubnet and node subnet facilitate this. However it does not support dual stack like overlay https://github.com/Azure/AKS/issues/3943 so you are confined to ipv4.

**Describe the solution you'd like**
Should be a able to give byo subnets that contain ipv6 addresses as a podsubnet and nodes should allocate a static block from those subnets to nodes.

**Describe alternatives you've considered**
Could do the same with node subnet.

**Additional context**
Add any other context or screenshots about the feature request here.