Check that PodDisruptionBudget has only one of maxUnavailable and minAvailable

I'm not sure how feasible it is to add a check for this but I noticed a PDB that has both values configured will be passed by Kubeconform (0.6.1).

https://kubernetes.io/docs/tasks/run-application/configure-pdb/
> You can specify only one of maxUnavailable and minAvailable in a single PodDisruptionBudget.