OBSDOCS-698: Update rhel8 to rhel9

Author: abrennan89

modules/cluster-logging-eventrouter-deploy.adoc

@@ -115,7 +115,7 @@ objects:
 parameters:
   - name: IMAGE <6>
     displayName: Image
-    value: "registry.redhat.io/openshift-logging/eventrouter-rhel8:v0.4"
+    value: "registry.redhat.io/openshift-logging/eventrouter-rhel9:v0.4"
   - name: CPU <7>
     displayName: CPU
     value: "100m"