alertmanager: give Alertmanager a persistent storage directory

playbooks/templates/chaosknoten/configs/grafana/compose.yaml.j2

@@ -25,6 +25,7 @@ services:
     volumes:
       - ./configs/alertmanager.yaml:/etc/alertmanager/alertmanager.yaml
       - ./configs/alertmanager_alert_templates.tmpl:/etc/alertmanager/templates/alert_templates.tmpl
+      - alertmanager_data:/alertmanager
 
   grafana:
     image: grafana/grafana
@@ -57,3 +58,4 @@ services:
 volumes:
   graf_data: {}
   prom_data: {}
+  alertmanager_data: {}