feat(examples): add multi-runner-v2 example

[edersonbrilhante]

Description

Adds the examples/multi-runner-v2 example for the unified experimental v2 interface.

• Demonstrates global defaults and per-lane runner, webhook, and compute-provider settings.
• Uses the v2 module inputs without the legacy v1 compatibility arguments.
• Adds example documentation, Terraform verification, provider locks, and navigation entries.

Test Plan

• terraform init -backend=false -input=false for examples/multi-runner-v2
• terraform validate for the example
• Terraform formatting, validation/TFLint, and merge-conflict checks

Related Issues

Depends on #5368, which depends on #5346.

[github-actions]

Dependency Review

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

Scanned Files

None