Alertmanager failed due to undefined receiver used in route

Issue

• Alertmanager pods keep restarting:

  $ oc get pods -n openshift-monitoring | grep alert
  NAME                                                    READY  STATUS   RESTARTS  AGE
  alertmanager-main-0                                     5/6    Running  6         8m40s
  alertmanager-main-1                                     5/6    Running  6         8m40s
  

• Alertmanager pods fail due to undefined receiver that is used in route :

  2023-08-08T05:32:38.614619853Z ts=2023-08-08T05:32:38.614Z caller=coordinator.go:118 level=error 
  component=configuration msg="Loading configuration file failed" 
  file=/etc/alertmanager/config_out/alertmanager.env.yaml err="undefined receiver \"Watchdog\" used in route"