Report aggregated cache stats for all cores on a Solr node

Solr caches are major memory consumers and Solr cache metrics are critical in memory tuning. However in current implementation, only cache metrics for individual collection is available. To get the same metrics for a collection alias, which may cover tens collections, the only way is to aggregate metrics from each collection for the collection alias manually or using an external tool.

The JIRA is to provide cache metrics for a collection alias to simplify the memory tuning for collection alias.