Add instructions to set up alerting channels to Prometheus example

prometheus/README.md

@@ -60,6 +60,13 @@ The provided `values.yaml` covers the following adjustments:
 - Client certificate injection to support scraping of workload secured with Istio strict mTLS
 - Active scraping of workload annotated with prometheus.io/scrape
 
+3. You can connect the Alertmanager to your notification channel (for instance, Slack or VictorOps) by providing an [Alertmanager configuration](https://prometheus.io/docs/alerting/latest/configuration/#configuration-file) to the `alertmanager.config` value.
+
+   The [alertmanager-values.yaml](./alertmanager-values.yaml) example provides a configuration that sends notifications for alerts with high severity to a Slack channel. To deploy it, download the file, adapt `<channel-name>`, `<api-url>` and `<cluster-domain>` to your environment, and run the Helm upgrade command to deploy the configuration:
+   ```bash
+    helm upgrade --install -n ${KYMA_NS} ${HELM_RELEASE} prometheus-community/kube-prometheus-stack -f https://raw.githubusercontent.com/kyma-project/examples/main/prometheus/values.yaml -f ./alertmanager-values.yaml --set grafana.adminPassword=myPwd
+   ```
+
 ### Activate scraping of Istio metrics & Grafana dashboards
 
 1. To configure Prometheus for scraping of the Istio-specific metrics from any istio-proxy running in the cluster, deploy a PodMonitor, which scrapes any Pod that has a port with name `.*-envoy-prom` exposed.

prometheus/alertmanager-values.yaml

@@ -0,0 +1,52 @@
+alertmanager:
+  config:
+   global:
+     resolve_timeout: 5m
+   inhibit_rules:
+     - source_matchers:
+         - 'severity = critical'
+       target_matchers:
+         - 'severity =~ warning|info'
+       equal:
+         - 'namespace'
+         - 'alertname'
+     - source_matchers:
+         - 'severity = warning'
+       target_matchers:
+         - 'severity = info'
+       equal:
+         - 'namespace'
+         - 'alertname'
+     - source_matchers:
+         - 'alertname = InfoInhibitor'
+       target_matchers:
+         - 'severity = info'
+       equal:
+         - 'namespace'
+   route:
+     group_by: ['namespace']
+     group_wait: 30s
+     group_interval: 5m
+     repeat_interval: 12h
+     receiver: 'null'
+     routes:
+     - receiver: 'null'
+       matchers:
+         - alertname =~ "InfoInhibitor|Watchdog"
+     - continue: true
+       match_re:
+         severity: critical
+       receiver: "slack"
+   receivers:
+   - name: 'null'
+   - name: "slack"
+     slack_configs:
+     - channel: "<channel-name>"
+       send_resolved: true
+       api_url: "<api-url>"
+       icon_emoji: ":ghost:"
+       title: '{{ template "__subject" . }}'
+       title_link: 'https://grafana.<cluster-domain>'
+       text: '{{ range .Alerts }}`}}<!channel>{{`{{- "\n" -}}`}}{{`{{ .Annotations.description }}`}}{{`{{- "\n" -}}`}}{{`{{ end }}'
+   templates:
+   - '/etc/alertmanager/config/*.tmpl'