Use amtool in the alertmanager pod instead of silencing job

docs/modules/ROOT/pages/how-tos/network/migrate-to-cilium.adoc

@@ -12,8 +12,17 @@
 
 IMPORTANT: Make sure that your `$KUBECONFIG` points to the cluster you want to migrate before starting.
 
-:duration: +120 minutes
-include::partial$create-alertmanager-silence-all-projectsyn.adoc[]
+. Silence all Project Syn alerts
++
+[source,bash]
+----
+silence_id=$(
+    kubectl --as=cluster-admin -n openshift-monitoring exec \
+    sts/alertmanager-main -- amtool --alertmanager.url=http://localhost:9093 \
+    silence add alertname!=Watchdog --duration="3h" -c "cilium migration"
+)
+echo $silence_id
+----
 
 . Select cluster
 +
@@ -268,4 +277,10 @@ include::partial$enable-argocd-autosync.adoc[]
 
 == Cleanup alert silence
 
-include::partial$remove-alertmanager-silence-all-projectsyn.adoc[]
+. Expire the silence
++
+[source,bash]
+----
+kubectl --as=cluster-admin -n openshift-monitoring exec sts/alertmanager-main --\
+    amtool --alertmanager.url=http://localhost:9093 silence expire $silence_id
+----