kube-prometheus: add alerting rules

assets/prometheus/rules/alertmanager.rules

assets/prometheus/rules/etcd2.rules

assets/prometheus/rules/etcd3.rules

assets/prometheus/rules/general.rules

assets/prometheus/rules/kube-apiserver.rules

assets/prometheus/rules/kube-controller-manager.rules

assets/prometheus/rules/kube-scheduler.rules

assets/prometheus/rules/kubelet.rules

assets/prometheus/rules/kubernetes.rules

assets/prometheus/rules/node.rules

assets/prometheus/rules/prometheus.rules

manifests/prometheus/prometheus-k8s-rules.yaml