Add Hybrid NAT support (#2261)

* Updates to support hybid NAT

* Fix readme

* Fix variable order

modules/net-vpc/variables.tf

@@ -1,5 +1,5 @@
 /**
- * Copyright 2023 Google LLC
+ * Copyright 2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -294,6 +294,18 @@ variable "subnets" {
   nullable = false
 }
 
+variable "subnets_private_nat" {
+  description = "List of private NAT subnets."
+  type = list(object({
+    name          = string
+    ip_cidr_range = string
+    region        = string
+    description   = optional(string)
+  }))
+  default  = []
+  nullable = false
+}
+
 variable "subnets_proxy_only" {
   description = "List of proxy-only subnets for Regional HTTPS or Internal HTTPS load balancers. Note: Only one proxy-only subnet for each VPC network in each region can be active."
   type = list(object({