[Stack Monitoring] [Test Scenario] Remote clusters

[simianhacker]

This involves running two separate clusters and connecting them together through the Remote Clusters feature in Kibana. The Stack Monitoring UI supports searching across remote clusters to show all known monitoring data.

Testing

• Ensure you can see a remote cluster's monitoring data in the Stack Monitoring UI
• Ensure the Stack Monitoring UI still works if that remote cluster is removed ([Monitoring] Fix UX around an unavailable remote cluster #79202)

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[estermv]

I see some errors in the Stack Monitoring UI after the remote cluster becomes unavailable:

These are the steps I followed to test this in staging:

1. I have two deployments: cluster-a and cluster-b, both with monitoring data enabled.
2. I go to cluster-b and add cluster-a in the Remote Clusters in Kibana
3. Stack Monitoring UI shows both deployments
4. I delete cluster-a deployment
5. In the Stack Monitoring UI still I see both deployments (I guess I visited the page too soon after deleting it)
6. When I reload the page, I see the errors from the screenshot and the page never loads

In the Remote Cluster Page the cluster appears as disconnected:

After removing the cluster-a from this page the Stack Monitoring UI works fine again.

[simianhacker]

@estermv I think the idea was to remove it form "Remote Clusters" instead of just deleting it (without removing it). I will change the wording.