Solr Cloud Graph screen blank

The Solr Admin UI - Cloud - Graph screen is blank. This was not an issue in Solr 9.2.1, so an API must have changed to make this no longer work.

After some investigation, the screen uses the Zookeeper API to look at clusterstate.json, so there must have been some back-compat logic in the Zookeeper API to make that work given that clusterstate.json no longer exists. This may no longer work.

As an easy fix, we can just move to using the Collections ClusterStatus API which returns the same data that used to exist in the clusterstate.json, so we don't even need to map fields or anything.