Question/Feature-Request: what is the correct method to get Indices health status (color)?

### Summary

I’d like to alert in Prometheus when **any index** changes health from green → yellow/red.  
The exporter provides cluster-level health (`elasticsearch_cluster_health_status{color=...}`), but I couldn’t find a **per-index** equivalent.

**Question:** Is there a way to get per-index health status from the exporter today?  
If not, I’d like to propose adding a metric for this.
