kube-prometheus: add custom-metrics-api example

manifests/custom-metrics-api/.gitignore

manifests/custom-metrics-api/README.md

...etrics-apiserver-auth-delegator-cluster-role-binding.yaml

...pi/custom-metrics-apiserver-auth-reader-role-binding.yaml

...stom-metrics-api/custom-metrics-apiserver-deployment.yaml

...trics-apiserver-resource-reader-cluster-role-binding.yaml

...metrics-api/custom-metrics-apiserver-service-account.yaml

.../custom-metrics-api/custom-metrics-apiserver-service.yaml

manifests/custom-metrics-api/custom-metrics-apiservice.yaml

...fests/custom-metrics-api/custom-metrics-cluster-role.yaml

...rics-api/custom-metrics-resource-reader-cluster-role.yaml

manifests/custom-metrics-api/deploy.sh

manifests/custom-metrics-api/gencerts.sh

...-metrics-api/hpa-custom-metrics-cluster-role-binding.yaml

manifests/custom-metrics-api/teardown.sh