Setup NAT for API cluster

[jakubno]

Note

Adds optional Cloud NAT for API nodes (with manual or auto static IPs), removes public IPs when enabled, and plumbs new variables through modules and Makefile.

• Network (Terraform):
  • Add Cloud Router and Cloud NAT for API nodes in nomad-cluster/network/main.tf, with MANUAL_ONLY allocation using api_nat_ips or auto-created addresses.
  • Enable NAT logging (errors only) and create-before-destroy lifecycle; parameterize by gcp_region.
• API Nodepool:
  • Make public IP assignment conditional in nomad-cluster/nodepool-api.tf (access_config removed when api_use_nat is true).
• Variables & Wiring:
  • Introduce api_use_nat (bool) and api_nat_ips (list) in variables.tf at root, nomad-cluster/variables.tf, and nomad-cluster/network/variables.tf; pass through in main.tf and nomad-cluster/main.tf (including gcp_region to network module).
  • Expose new TF_VARs in iac/provider-gcp/Makefile.

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[linear]

ENG-2304 Setup NAT for our cluster