[Feature] Azure CNI Overlay - add support for extending Service CIDR

Hi,

**Is your feature request related to a problem? Please describe.**
Currently we can't change the Service CIDR for an existing AKS cluster using Azure CNI Overlay. This is an issue because if a cluster has been created with an address space which is too small, we'll have to create a new cluster.

**Describe the solution you'd like**
I'd like to be able to extend the Service CIDR for an existing cluster / or add more than one CIDR.

**Describe alternatives you've considered**
Since it can only be set at the cluster creation, there is are no other alternatives.

**Additional context**
Kind of the same issue as #4368

Thanks.