kerr: ProducerFenced is not retriable

This could result in AddPartitionsToTxn silently stripping batches to be
produced. It would look like the client was hanging, when in reality we
need to notify the user the client is in a fatal state.

pkg/kerr/kerr.go

@@ -163,7 +163,7 @@ var (
  InvalidRecord = &Error{"INVALID_RECORD", 87, false, "This record has failed the validation on broker and hence be rejected."}
  UnstableOffsetCommit = &Error{"UNSTABLE_OFFSET_COMMIT", 88, true, "There are unstable offsets that need to be cleared."}
  ThrottlingQuotaExceeded = &Error{"THROTTLING_QUOTA_EXCEEDED", 89, true, "The throttling quota has been exceeded."}
- ProducerFenced = &Error{"PRODUCER_FENCED", 90, true, "There is a newer producer with the same transactionalId which fences the current one."}
+ ProducerFenced = &Error{"PRODUCER_FENCED", 90, false, "There is a newer producer with the same transactionalId which fences the current one."}
  ResourceNotFound = &Error{"RESOURCE_NOT_FOUND", 91, false, "A request illegally referred to a resource that does not exist."}
  DuplicateResource = &Error{"DUPLICATE_RESOURCE", 92, false, "A request illegally referred to the same resource twice."}
  UnacceptableCredential = &Error{"UNACCEPTABLE_CREDENTIAL", 93, false, "Requested credential would not meet criteria for acceptability."}