refactor(templates): use aws-region and aws-ec2-instance-type modules across AWS templates

[phorcys420]

Adopts the maintained aws-region and aws-ec2-instance-type modules across the AWS starter templates (aws-linux, aws-windows, aws-envbuilder), replacing hand-rolled region and instance_type coder_parameter blocks with the shared modules.

Per template

• aws-linux / aws-windows: replace both hand-rolled region and instance_type parameters with module "aws_region" (~> 1.1) and module "aws_ec2_instance_type" (~> 1.0).
• aws-envbuilder: already consumed aws_region; bump it ~> 1.0 → ~> 1.1 and replace the hand-rolled instance_type parameter with module "aws_ec2_instance_type" (~> 1.0).

Details

• availability_zone now comes from the new module.aws_region.default_availability_zone output (added in aws-region v1.1.0) instead of interpolating "${region}a" — identical value.
• aws-ec2-instance-type defaults to t3.micro with the default include = ["t3"] family.

Parameter key changes

The modules hardcode their parameter names, so the stable parameter keys change:

• region → aws_region
• instance_type → aws_ec2_instance_type

Defaults are preserved (us-east-1, t3.micro), so fresh builds are unaffected. The region list grows 17 → 29 and the instance-type picker gains t3.nano; the previous options remain a subset, nothing is removed. The coder_metadata display items keep their own key values, which are unrelated to the parameter names.

Context / decision log

Goal: replace the hand-rolled region / instance-type coder_parameter blocks in the AWS starter templates with the maintained aws-region and aws-ec2-instance-type modules, matching aws-envbuilder's existing region-module usage and cutting duplicated 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 — aws-linux, aws-windows, and aws-envbuilder main.tf. No module source changes.

Versions:

• aws-region pinned ~> 1.1 (v1.1.0 introduces the default_availability_zone output used here); resolves to 1.1.0.
• aws-ec2-instance-type pinned ~> 1.0; resolves to 1.0.0.

Behavior preservation:

• Defaults unchanged: region us-east-1, instance type t3.micro; mutable = false preserved (module defaults).
• availability_zone: module.aws_region.default_availability_zone returns "<region>a", identical to the old interpolation.
• Region options 17 → 29; instance types gain t3.nano; previous options are subsets, so nothing is removed.
• No README references the removed parameters, so no README changes were needed.

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

Out of scope (separate follow-up): wiring the windows-rdp module into aws-windows. That template 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.

Solves #1122

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Generated by Coder Agents on behalf of @phorcys420.

[matifali]

LGTM. Thanks for doing this. Templates look way, more cleaner now.