fix: validates NUTANIX_ENDPOINT does not fall in the Load Balancer IP Range

[manoj-nutanix]

webhook errors out if NUTANIX_ENDPOINT IP falls in Load Balancer IP Range. It only implements dumb check which compares PC IP with Load Balancer IP Range. It's complex to achieve with CEL so going with webhook as we'll need to use regex(isIP() func is not working for cluster variables) to extract IP from PC URL and do string compare which not robust as we can do error handling through webhook.

What problem does this PR solve?:

Which issue(s) this PR fixes:
Fixes #
https://jira.nutanix.com/browse/NCN-102628

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-addonexport-dockerhub-credentials serverside-applied
secret/nutanix-cluster-cilium-helm-addonexport-pc-creds-for-csi serverside-applied
Warning: Detected changes to resource nutanix-cluster-cilium-helm-addonexport-pc-creds which is currently being deleted.
secret/nutanix-cluster-cilium-helm-addonexport-pc-creds serverside-applied
Error from server (Forbidden): admission webhook "cluster-validator.caren.nutanix.com" denied the request: prism central IP "198.18.1.1" must not be part of MetalLB address range "198.18.1.1"-"198.18.1.10"

[jimmidyson]

Recently noticed that net/netip has improved functions for parsing IPs (errors instead of nil slices if not an IP!) and netipx has really useful functions for handling ranges.

[manoj-nutanix]

Closing this PR in favor of #1001 as forked repos don't have access to github secrets so some e2e tests failing.