Refresh example: pin modules to 1.7.2, bump aws provider to ~> 6.0

examples/main.tf pinned the modules at the stale ref=1.3.0 and the root
aws provider at ~> 5.0. With the cnames provider fix shipped in 1.7.2,
the documented quilt + cnames topology resolves on ~> 6.0; bump both
module refs to 1.7.2 and the root provider to ~> 6.0 so the example
inits cleanly (verified: resolves to aws v6.49.0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: sir-sigurd

examples/main.tf

@@ -45,7 +45,7 @@ terraform {
   required_providers {
     aws = {
       source  = "hashicorp/aws"
-      version = "~> 5.0"
+      version = "~> 6.0"
     }
   }
 }
@@ -83,7 +83,7 @@ variable "okta_client_secret" {
 # Main Quilt module
 module "quilt" {
   # Pin to the latest stable version from https://github.com/quiltdata/iac/tags
-  source = "github.com/quiltdata/iac//modules/quilt?ref=1.3.0"
+  source = "github.com/quiltdata/iac//modules/quilt?ref=1.7.2"
 
   name          = local.name
   template_file = local.build_file_path
@@ -199,7 +199,7 @@ module "quilt" {
 
 # DNS configuration (optional but recommended)
 module "cnames" {
-  source = "github.com/quiltdata/iac//modules/cnames?ref=1.3.0"
+  source = "github.com/quiltdata/iac//modules/cnames?ref=1.7.2"
 
   lb_dns_name    = module.quilt.stack.outputs.LoadBalancerDNSName
   quilt_web_host = local.quilt_web_host