feat(orchestration-providers): add webhook provider modules

[edersonbrilhante]

Description

Adds the internal webhook orchestration-provider module, including scale-up, scale-down, pool reconciliation, job retry, IAM policies, logging, validation, and provider outputs.

The module consumes the selected compute provider’s contract and keeps provider-specific orchestration resources separate from shared runner configuration and provider selection.

Test Plan

• Repository Terraform formatting, validation/TFLint, and merge-conflict checks
• Webhook, scale-runner, pool, and job-retry Terraform tests are included in the PR
• Local provider-plugin handshake prevented a complete test run on macOS arm64

Related Issues

Depends on #5343.

[github-actions]

Dependency Review

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

Scanned Files

None

[Brend-Smits]

Reviewed the webhook orchestration-provider split. Verified the scale-up lambda env-var contract is preserved exactly, v1's 41 keys equal the union of the 30 kept here and the 11 supplied by the EC2 provider contract (0 dropped / 0 added).

One cross-stack note: scale-up/scale-down here still use the colon-joined PARAMETER_GITHUB_APP_* list transport (#5282), which the in-flight manifest PR replaces; whichever lands second will need to reconcile, and the v2 duplication means that fix has to be applied here too.