Support multiple NICs on vSphere clusters

**What would you like to be added**:
CAPV exposes the capability to create vms with multiple network interfaces with this api [here](https://github.com/kubernetes-sigs/cluster-api-provider-vsphere/blob/cc840c560ec33f378aa1ea9dc9294eceba52b4b9/apis/v1beta1/types.go#L241). Currently EKS-A cluster spec doesn't provide a way to include more than one network for the vms getting created. We should open up this feature for users looking to create vms that span across multiple networks.

**Why is this needed**:
As a general practice, users isolate storage networks from the general traffic. In order to support use cases like this, we need to provide a way to allow multiple networks on our cluster spec.

Start with the CAPV API reference in apis/v1beta1/types.go linked in the issue, then trace EKS-A's cluster spec and vSphere VM network handling. Done means users can declare multiple networks in the cluster spec and those networks are applied to created VMs; run the relevant repository tests after locating them.

Written by the indexing model from the issue text.