The PDB was added in: #471

Not all users are going to want to use a PodDisruptionBudget when running Solr.
The feature should be able to be disabled/enabled via the SolrCloud CRD.

When looking at #471, there are other options we might want to add like PDBs per-pod.
So whatever field we add to the CRD should be expandable to customize other parts of the PDB creation/management.