[Feature] Azure CNI Overlay - configurability of currently fixed /24 address space for pods

Azure CNI Overlay currently has fixed pod density per node, as noted in the documentation

> The Overlay solution assigns a /24 address space for pods on every node from the private CIDR that you specify during cluster creation. The /24 size is fixed and can't be increased or decreased [[1]](https://learn.microsoft.com/en-us/azure/aks/azure-cni-overlay?tabs=kubectl#ip-address-planning).

This setting, even with fairly large Pod CIDR, can be main limiting factor for number of nodes per AKS cluster. For example /16 Pod CIDR can contain maximum of 256 nodes.

**Describe the solution you'd like**
I would like to be able to change this mask, e.g. to /25 or /26 - to get more flexibility in IP address space management. Depending on use case, workload type and scale, different pod densities are needed. Ideally, changing this mask should be supported for existing AKS clusters.

**Describe alternatives you've considered**
Alternative solution would be to overcome this limitation with using larger Pod CIDR. But very broad CIDR can result in overlapping ranges and problems with network peering.
Also, Pod CIDR cannot be extended for an existing cluster [[2]](https://github.com/Azure/azure-cli/issues/28403), so this would be viable only in foresight.

**Additional context**
[1] https://learn.microsoft.com/en-us/azure/aks/azure-cni-overlay?tabs=kubectl#ip-address-planning
[2] https://github.com/Azure/azure-cli/issues/28403