Pod Disruption Budgets can help to ensure that only limited number of pods can be terminated because of voluntary evictions (e.g. draining a node for maintenance etc.). This PR adds support for Pod Disruption Budgets to the Cluster Operator. It will automatically create the PodDisruptionBudget resources for Kafka and Zookeeper statefulsets and Connect and Mirror Maker deployments. By default, it will allow only one pod to be down at a time. Users can use the templates to change this number (either increase the number or set it to 0 to handle the evictions manually only).