Expose index uuid in _stats endpoint #31791
Description
To collect metrics about the Elasticsearch indices Metricbeat calls the /_stats endpoint. Inside the object "indices" : { all indices are listed with its names. The data that is missing inside is the index uuid. It can be fetched by calling GET /index-name and then can be found under uuid. Having to make a separate request for each index to fetch the identifier is not an optimal solution.
The uuid is important for the following reasons:
- The same index name can exist in multiple clusters. Beats can collect data from multiple clusters into a single monitoring cluster.
- An index can be deleted and a new one created with the same name. In this case only the UUID is different.
- With cross cluster replication matching indices from 2 different clusters with the same uuid could become even more interesting: Introduce cross-cluster replication #30086
NOTE: The _stats endpoint also currently does not expose the cluster_uuid and we fetch it in a separate call.