Proposed title of this feature request

Support to specify the subnet for Kubernetes "service type" Load Balance

What is the nature and description of the request?

Allow to specify subnet for ilb . Enable this https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/legacy-cloud-providers/gce/gce_annotations.go#L64

Why does the customer need this? (List the business requirements here)

Customer needs custom ILBs to be created from a specific subnet to allocate IPs

List any affected packages or components.

OpenShift GCP custom Ingress Controller