GET /_license/feature_usage returns only node-local information

[DaveCTurner]

A license is a cluster-wide concept, but today the GET /_license/feature_usage API returns only details about the licensed features used by the node handling the request. Thus if the caller wants to know about the features used by the whole cluster they must query this API on every node separately and then manually aggregate the results.

This is rather confusing, and is inconsistent with most other APIs regarding cluster-wide concepts which do the work needed to build a cluster-wide response themselves.

Could we make this API more like other cluster-level APIs?

[elasticsearchmachine]

Pinging @elastic/es-security (Team:Security)