Add pdb configuration

[nirroz93]

add option in the configuration to create podDisruptionBudget, so master and replica won't be down at the same time. Maybe even set default when there is a replica

[cmergenthaler]

I think it would be nice if the PDB is dynamically changed by the operator, so that a disruption of the master is only allowed if there is at least 1 replica in full sync with the master. Otherwise it could happen that the master is evicted too early by k8s and the cache is gone.