feat(scale-set): add scale set orchestration in Terraform

[edersonbrilhante]

Description

Adds the internal scale-set orchestration provider for experimental multi-runner v2. It groups runner configurations into controller groups, with grouping by compute-provider type, runner configuration, or explicit custom membership, and validates ownership uniqueness across normalized GitHub URL and scale-set ID pairs.

For each controller group, the module creates the ECS Fargate cluster/service/task definition, task and execution roles, log group, security group, and controller runtime configuration. It writes one non-secret SSM reconciler parameter per runner configuration, passes only credential parameter references to the task, applies the selected compute-provider's opaque runtime and IAM contract, and validates plan-known grouping, configuration size, and IAM policy limits. The module adopts existing GitHub scale sets; it does not create or delete the GitHub scale-set resources themselves.

Test Plan

• Ran terraform fmt -check -recursive
• Repository Terraform pre-commit validation passed during commit.

Related Issues

None.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None