feat: support additional pod ranges and per-node-pool pod_range mapping

[ciiiii]

Motivation

Extend the GKE wrapper to support additional secondary pod IP ranges, so operators don't have to create overflow node pools manually via gcloud (which causes terraform drift on every plan).

Upstream module: terraform-google-modules/kubernetes-engine v35.0.1 already exposes additional_ip_range_pods (used to populate additional_pod_ranges_config.pod_range_names on the cluster) and a per-pool pod_range, but this wrapper doesn't surface either.

Modifications

• variables.tf:
  • New additional_pod_range_names (list(string), default []) — names of additional secondary pod ranges to attach to the cluster.
  • New node_pool_pod_range_mapping (map(string), default {}) — per-pool override for pod_range, keyed by node-pool name.
• main.tf:
  • Pass additional_ip_range_pods = var.additional_pod_range_names to module.gke.
  • default_node_pool_config.pod_range and func_pool_config.pod_range now look up var.node_pool_pod_range_mapping[<pool-name>], falling back to var.secondary_ip_range_pods (the primary).
• README.md: regenerated via terraform-docs.

Both new variables default to empty / no-op so existing consumers are unaffected.