Upgrade and improve AWS Terraform example

• Bump JFrog Platform chart to 11.5.0, metrics-server chart to 3.12.2 (pinned), Kubernetes to 1.35, PostgreSQL to 17.7
• Replace ~15 repeated sizing ternary chains with a single locals.tf sizing map (local.s.*) — adding a new tier now requires editing
  one block
• Remove hardcoded database password defaults; passwords must now be set explicitly in terraform.tfvars (validated at plan time)
• Fix null_resource chart fetch to re-run when chart version changes (was missing triggers)
• Parameterize EKS root volume size/throughput and S3 force_destroy
• Add description to all variables that lacked one