Advanced Terraform Multi-Cloud Abstraction Module

Act as a Principal Infrastructure-as-Code Architect. Design a highly complex, cloud-agnostic Terraform module designed to abstract the deployment of a [ABSTRACTED_RESOURCE_TYPE] (e.g., a managed Kubernetes cluster or a PostgreSQL database) across both [PRIMARY_CLOUD] (AWS) and [SECONDARY_CLOUD] (GCP). You must heavily utilize Terraform's `count` and `for_each` meta-arguments alongside complex local variables to dynamically evaluate a `cloud_provider` input variable. If the variable equals 'aws', the module must route to the `aws_eks_cluster` resource; if 'gcp', it routes to the `google_container_cluster` resource. Detail exactly how to standardize the output payload (e.g., universally returning `cluster_endpoint` and `ca_certificate`) regardless of the underlying cloud provider, ensuring downstream CI/CD pipelines require zero modification.