VAULT-28146: Add IPV6 support to enos scenarios (#27884)

* VAULT-28146: Add IPV6 support to enos scenarios

Add support for testing all raft storage scenarios and variants when
running Vault with IPV6 networking. We retain our previous support for
IPV4 and create a new variant `ip_version` which can be used to
configure the IP version that we wish to test with.

It's important to note that the VPC in IPV6 mode is technically mixed
and that target machines still associate public IPV6 addresses. That
allows us to execute our resources against them from IPV4 networks like
developer machines and CI runners. Despite that, we've taken care to
ensure that only IPV6 addresses are used in IPV6 mode.

Because we previously had assumed the IP Version, Vault address, and
listener ports in so many places, this PR is essentially a rewrite and
removal of those assumptions. There are also a few places where
improvements to scenarios have been included as I encountered them while
working on the IPV6 changes.

Signed-off-by: Ryan Cragun <me@ryan.ec>

enos/modules/create_vpc/variables.tf

@@ -7,10 +7,21 @@ variable "name" {
   description = "The name of the VPC"
 }
 
-variable "cidr" {
+variable "ip_version" {
+  type        = number
+  default     = 4
+  description = "The IP version to use for the default subnet"
+
+  validation {
+    condition     = contains([4, 6], var.ip_version)
+    error_message = "The ip_version must be either 4 or 6"
+  }
+}
+
+variable "ipv4_cidr" {
   type        = string
   default     = "10.13.0.0/16"
-  description = "CIDR block for the VPC"
+  description = "The CIDR block for the VPC when using IPV4 mode"
 }
 
 variable "environment" {