feat(scale-set): wire orchestration through runner config

[edersonbrilhante]

Description

Wire scale-set orchestration through the provider-aware Terraform composition.

• Resolve global and per-lane scale-set settings into the canonical runner configuration.
• Route scale-set lanes through runner-config and the scale-set orchestration provider.
• Extend the EC2 provider contract with the scale-set runtime configuration, IAM fragments, and outputs consumed by the controller.
• Gate webhook resources by the selected orchestration provider.
• Add scale-set validation and Terraform coverage across the affected modules.

This PR provides the Terraform wiring used by the scale-set example and the later MiniStack integration PRs.

Test Plan

• Terraform formatting, validation/TFLint, and merge-conflict checks passed through the repository hooks.
• Scale-set routing and configuration-resolution tests passed.
• Multi-runner and runner-config scale-set Terraform tests passed.
• Native provider tests remain subject to the local macOS arm64 plugin-handshake limitation.

Related Issues

Depends on #5299.

[github-actions]

Dependency Review

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

Scanned Files

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[guicaulada]

Nice work wiring this together! Looks good overall, but we should handle the case where the installation ID is omitted. I’ve left a comment inline.