[AutoOps] Use `cluster.metadata.display_name` for Cloud Connected Cluster Name

[pickypg]

When we register the cluster, we should supply the name as the cluster's "display name", if one is set:

beats/x-pack/metricbeat/module/autoops_es/metricset/register.go

Line 121 in d85c675

Name: clusterInfo.ClusterName,

The cluster.metadata.display_name is a supported metadata name where tools, such as ECE, will set the name that the user has dynamically determined for the cluster. This can be used to override the unchangeable cluster.name setting.

This is set via the _cluster/settings API and is, traditionally, only concerned with the persistent setting, but naturally it could also be a transient setting (with a lot less value).

[pickypg]

#47438 relates to this issue, but from a different context. That involves shipping the data (which we already do), but we need the AutoOps backend to use it.

[steevo590]

Would really like to see this implemented in autoops, I have around 40 clusters so trying to remember which of the 40 different random string of letters and number is the cluster I want to look at is a little difficult