Minor Description
Cluster properties is a good place to store configuration data that's shared in the whole cluster: solr and other (authorized) apps can easily read and update them.
It would be very useful if we can store extra data in cluster properties which would act as a centralized property management system between solr and its related apps (like manager or monitor apps).
And the change would be also very simple.
We can also require all extra property starts with prefix like: extra_
PR: https://github.com/apache/lucene-solr/pull/429