// MatchConstraints specifies what resources this policy is designed to validate.
  // The AdmissionPolicy cares about a request if it matches _all_ Constraints.
  // However, in order to prevent clusters from being put into an unstable state that cannot be recovered from via the API
  // ValidatingAdmissionPolicy cannot match ValidatingAdmissionPolicy and ValidatingAdmissionPolicyBinding.
  // Required.
  optional MatchResources matchConstraints = 2;