Cloud-on-k8s: Elasticsearch client leak

[barkbay]

There is an Elasticsearch client leak in the Elasticsearch driver:

https://github.com/elastic/cloud-on-k8s/blob/e0773830c8ab5a40a2881e6c7bc1226d89da1520/pkg/controller/elasticsearch/driver/driver.go#L165-L173

In most cases the client created for the observer is never closed, leading to a memory leak.

[pebrc]

I wonder if this would suffice as a fix:

diff --git a/pkg/controller/elasticsearch/observer/manager.go b/pkg/controller/elasticsearch/observer/manager.go
index 29dc54ea..2921e048 100644
--- a/pkg/controller/elasticsearch/observer/manager.go
+++ b/pkg/controller/elasticsearch/observer/manager.go
@@ -49,6 +49,7 @@ func (m *Manager) Observe(cluster types.NamespacedName, esClient client.Client)
                m.StopObserving(cluster)
                return m.createObserver(cluster, esClient)
        default:
+               esClient.Close()
                return observer
        }
 }