Delete Managed Kube resources that are no longer used

The Solr Operator creates many Kubernetes resources while reconciling.

The operator will often choose to create or not create resources depending on the configuration of Solr resource (e.g. a SolrCloud resource). However if a SolrCloud is setup in a way that a resource is needed, and then the setup is changed so the resource is no longer necessary, the operator does not go and garbage collect that resource.

It would be nice to add this additional level of garbage collection to the operator.

We could possibly design this in a way to auto-collect at the end of a reconcile, or just do it on a case-by-case basis for each resource dependency.

Start by tracing the operator's reconcile flow and inventory the Kubernetes resources it conditionally creates for a SolrCloud. Determine how to identify resources that are no longer needed and whether cleanup belongs at the end of reconciliation or with each resource dependency. Done means obsolete resources are garbage-collected while still-needed resources remain managed.

Written by the indexing model from the issue text.