KAFKA-20662: Throw INCONSISTENT_GROUP_PROTOCOL for malformed request during online migration

[dongnuo123]

When the subscription deserialization fails, we throw an
IllegalStateException

private static ConsumerProtocolSubscription deserializeSubscription(
  JoinGroupRequestProtocolCollection protocols
) {
  try {
  return ConsumerProtocol.deserializeConsumerProtocolSubscription(
    ByteBuffer.wrap(protocols.iterator().next().metadata()));
  }
  catch (SchemaException e) {
  throw new IllegalStateException("Malformed embedded consumer protocol
in subscription deserialization.");
  }
}

which will be translated to UNKNOWN_SERVER_ERROR. This is a bit
confusing to the client. We throw a fatal INCONSISTENT_GROUP_PROTOCOL
here instead.