Document license rotation

[pebrc]

The orchestration Enterprise license contains multiple shorter lived cluster licenses that the operator adds to the Elasticsearch clusters it orchestrates. This can be confusing to users who then see a license expiration date in Kibana that is much shorter than the orchestration level license. Of course the operator will configure a new license once the initial cluster license expires so that there is no real reason for concern.

We should document this behaviour, and maybe consider the overall expiry in the elastic-licensing ConfigMap that the operator populates with license related usage data. https://www.elastic.co/guide/en/cloud-on-k8s/current/k8s-licensing.html#k8s-get-usage-data

[pebrc]

Fixed with #4517