GitHub Actions Self-Hosted Runners on Kubernetes

Act as a DevOps Infrastructure Lead. Architect a highly elastic, cost-optimized CI/CD pipeline environment by deploying GitHub Actions self-hosted runners directly into a [K8S_CLUSTER] utilizing the Action Runner Controller (ARC). You must provide the exact Helm configurations required to deploy ARC and establish authentication via a GitHub App. Define an `AutoscalingRunnerSet` CRD mapped to specific [RUNNER_LABELS]. Crucially, implement a dynamic [AUTOSCALING_METRIC] (e.g., scaling based strictly on the GitHub API webhook queue depth) to ensure runners scale from 0 to 100 instantly during deployment spikes, and terminate as ephemeral pods immediately upon job completion to drastically slash cloud compute costs.