`kubernetes autoscaling` feature (baseline)

[jfallows]

Baseline

• Support zilla.yaml as alternative to zilla.json for improved dev ops alignment
• Integrate ConfigMap with entire zilla.yaml configuration in a single key
  • automatically detect changes to ConfigMap via zilla configuration file watcher
• Support ${{ env.SECRET_VAR }} syntax to integrate Kubernetes secrets via environment variables
• Verify Kubernetes HPA custom metric -> prometheus adapter -> Prometheus -> Zilla prometheus exporter
• kubernetes.prometheus.autoscale example zilla-examples#41