fix: validates CONTROL_PLANE_ENDPOINT_IP and NUTANIX_ENDPOINT are distinct

[manoj-nutanix]

What problem does this PR solve?:
webhook errors out if NUTANIX_ENDPOINT IP is same as PC IP. It only implements dumb check which compares PC IP with control-plane IP.

Which issue(s) this PR fixes:
Fixes #
https://jira.nutanix.com/browse/NCN-102626

How Has This Been Tested?:

Special notes for your reviewer:

 clusterctl generate cluster ${CLUSTER_NAME} \   
  --from ${CLUSTER_FILE} \
  --kubernetes-version ${KUBERNETES_VERSION} \
  --worker-machine-count 1 | \
  kubectl apply --server-side -f -
secret/nutanix-cluster-cilium-helm-addon-dockerhub-credentials serverside-applied
secret/nutanix-cluster-cilium-helm-addon-pc-creds-for-csi serverside-applied
Warning: Detected changes to resource nutanix-cluster-cilium-helm-addon-pc-creds which is currently being deleted.
secret/nutanix-cluster-cilium-helm-addon-pc-creds serverside-applied
Error from server (Forbidden): admission webhook "cluster-validator.caren.nutanix.com" denied the request: prism central and control plane endpoint cannot have the same IP "10.47.10.4"

[dkoshkin]

Looking good, just a few comments

[dkoshkin]

Thanks!

[dkoshkin]

nit: returning an empty struct here instead of nil kinda smells

[manoj-nutanix]

yeah, looks weird at first.. I just followed net/netip pkg semantic, maybe Addr struct doesn't hold much data so they return empty struct instead of nil everywhere.