feat: Virtual IP configuration to set different address/port

[dkoshkin]

What problem does this PR solve?:
New configuration to support setting different virutalIP address from the external controlPlaneEndpoint. This is useful for Clusters like a Nutanix Cluster in a VPC where the virtual IP needs to be some IP from same Subnet as the VMs, but the conrtol-plane endpoint is a floating IP mapped to the virtual IP accessible from outside the VPC.

spec:
  topology:
    variables:
      - name: clusterConfig
        value:
          nutanix:
            controlPlaneEndpoint:
              host: x.x.x.x
              port: 6443
              virtualIP:
                configuration:
                  address: y.y.y.y

The "configuration" keyword comes from an existing API here

cluster-api-runtime-extensions-nutanix/api/v1alpha1/addon_types.go

Line 260 in 8e2b307

Configuration *ServiceLoadBalancerConfiguration `json:"configuration,omitempty"`

Which issue(s) this PR fixes:
Fixes #

How Has This Been Tested?:

• New unit tests
• Created a Nutanix Cluster inside a VPC

Assigned a floating IP 10.22.198.34 to an internal IP 172.16.0.101

One of the control-plane VMs got the internal VIP assigned.

And the Cluster is accessible outside of the VPC.

kubectl get nodes
NAME                                          STATUS   ROLES           AGE    VERSION
dkoshkin-floating-ip-k9d74-d8jxp              Ready    control-plane   122m   v1.30.5
dkoshkin-floating-ip-k9d74-fb5pb              Ready    control-plane   125m   v1.30.5
dkoshkin-floating-ip-k9d74-wtl5w              Ready    control-plane   123m   v1.30.5
dkoshkin-floating-ip-md-0-qkg7q-pm5z9-6zf8f   Ready    <none>          124m   v1.30.5

Special notes for your reviewer:

[supershal]

LGTM

[jimmidyson]

@dkoshkin Do we know of other providers that would need to support this? If not, then I wonder if we should make it specific to Nutanix clusters somehow.

[jimmidyson]

Actually just realised that Nutanix CCM handler will need updating in https://github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/blob/main/pkg/handlers/generic/lifecycle/ccm/nutanix/handler.go to pass in this VIP as well to be ignored as part of possible node IPs by Nutanix CCM.