Use the new cluster.metadata feature introduced into ES to allow the cluster name to be semi-dynamic by accepting cluster.metadata.display_name as an alternative to cluster_name. If cluster.metadata.display_name is unset, then it should fall back to cluster_name.

This will enable multiple use cases surrounding the cluster name:

1. Fixing cluster's named elasticsearch because they were not named upfront.
2. Enabling Elastic Cloud to show a different name for the cluster from the default UUID-based names.
3. Providing a mechanism for users to change their cluster's name as needed (e.g., with the introduction of CCS/CCR it may be useful to add a region to a cluster's name).

Relates to elastic/elasticsearch#33325 (merged)