Remove Snitch. Simplify NodeStateProvider usage.

The NodeStateProvider is a relic relating to the old autoscaling framework that was removed in Solr 9.  The only remaining usage of it is for SplitShardCmd to check the disk space.  For this, it could use the metrics api. (Update: keep NodeStateProvider albeit simplify the default impl by removing Snitch stuff. Add "NodeValueFetcher").

I think we'll observe that Snitch and other classes in org.apache.solr.common.cloud.rule can be removed as well, as it's related to NodeStateProvider.

Only org.apache.solr.cluster.placement.impl.AttributeFetcherImpl#getMetricSnitchTag and org.apache.solr.cluster.placement.impl.NodeMetricImpl refer to some constants in the code to be removed.  Those constants could move out, consolidated somewhere we think is appropriate.