Cluster license cannot be updated by ECK if it has already expired

[pebrc]

Related #5796

With the changes from above mentioned PR it is no longer possible to update the cluster license if the currently installed license has already expired because the reachability criterion relies on a successful health observation:

https://github.com/elastic/cloud-on-k8s/blob/2.5/pkg/controller/elasticsearch/driver/driver.go#L243

We need to distinguish the two criteria (service has endpoints and health API responds).

However it seems with expired license health observations are no longer possible as the health API is blocked in the degraded state Elasticsearch enters into when the license expires.

One potential fix for this issue is therefore only apply the first criteria (service has endpoints) when deciding whether to try the license API call or not.

Workarounds:

• manually install the license contained in the Kubernetes secret called $CLUSTER_NAME-es-license via curl https://www.elastic.co/guide/en/elasticsearch/reference/current/update-license.html (that's all the operator does anyway)
• revert to a Basic license which will re-enable the operator to apply the correct license https://www.elastic.co/guide/en/elasticsearch/reference/current/start-basic.html (CAVEAT: I don't know if that has negative non-reversible effects on features in use)