Inadvertent peering of alertmanager instances during upgrade

Cluster and userworkload alertmanager instances inadvertenly become peered during upgrade

infrequently - customer observed this on 3 cluster out of 15 

Deploy userworkload monitoring 

~~~
 config.yaml: |
    enableUserWorkload: true
    prometheusK8s:
~~~

Deploy user workload alertmanager  

~~~
  name: user-workload-monitoring-config
  namespace: openshift-user-workload-monitoring
data:
  config.yaml: |
    alertmanager:
      enabled: true 
~~~

upgrade the cluster
verify the state of the alertmanager clusters: 

~~~
$ oc exec -n openshift-monitoring alertmanager-main-0 -- amtool cluster show -o json --alertmanager.url=http://localhost:9093
~~~

alertmanager show 4 peers

we should have 2 pairs 

Mitigation steps: 

Scaling down one of the alertmanager statefulsets to 0 and then scaling up again restores the expected configuration (i.e. 2 separate alertmanager clusters)

- the customer then added networkpolicies to prevent alertmanager gossip between namespaces.