refactor(templates): use aws-region module in aws-linux and aws-windows

[phorcys420]

Adopts the maintained aws-region module in the aws-linux and aws-windows starter templates, replacing the duplicated hand-rolled coder_parameter "region" block. This matches what aws-envbuilder already does and drops ~90 lines of duplicated region option data per template.

Changes (per template)

• Replace the region coder_parameter (17 static options) with module "aws_region" (pinned ~> 1.0, default = "us-east-1").
• Repoint the aws provider region, the instance availability_zone, and the region metadata item to module.aws_region.value.

Note: parameter key changes region → aws_region

The module hardcodes the parameter name = "aws_region" (the old block used region), so the stable parameter key changes. default = "us-east-1" preserves the same default selection, so fresh builds are unaffected. The region list grows 17 → 29 (the old options are a subset, nothing removed). The coder_metadata display item keeps its own key = "region", which is unrelated to the parameter name.

Context / decision log

Goal: replace the hand-rolled data "coder_parameter" "region" block in the two AWS templates with the maintained aws-region module, matching aws-envbuilder. Consistency + less duplicated region option data. AWS was the only cloud where region-module adoption was inconsistent (every GCP and Azure template already consumes its region module).

Scope: templates only — registry/coder/templates/aws-linux/main.tf and registry/coder/templates/aws-windows/main.tf. No module version bump (nothing under registry/**/modules/ changes).

Module interface: aws-region exposes default / mutable / exclude / … inputs and a value output; internally it declares data "coder_parameter" "region" with name = "aws_region" and 29 regions. Pinned ~> 1.0 (same as aws-envbuilder), resolves to 1.0.31.

Behavior preservation:

• Default stays us-east-1 (set on the module).
• mutable = false preserved (module default).
• availability_zone keeps the "<region>a" suffix.
• Region list 17 → 29; the original 17 are a subset of the 29, so nothing is removed.
• No README references the removed parameter, so no README changes were needed.

Validation: terraform init + terraform validate pass for both templates; terraform fmt and prettier --check are clean.

Out of scope (separate follow-up): wiring the windows-rdp module into aws-windows. That template currently has no admin-password plumbing (its user_data only bootstraps the agent), so adding windows-rdp means introducing a random_password, setting the Windows Administrator password in user_data, and passing admin_username / admin_password — a bigger, template-specific change kept out of this PR.

---

Generated by Coder Agents on behalf of @phorcys420.