alerting rules: replace severity with action

assets/prometheus/rules/alertmanager.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/node.rules

assets/prometheus/rules/prometheus.rules