code: public static byte[] getConsumerStateColumn(long groupId, int instanceId) {
      byte[] column = new byte[Longs.BYTES + Ints.BYTES];
      Bytes.putLong(column, 0, groupId);
      Bytes.putInt(column, Longs.BYTES, instanceId);
      return column;
    }
docs: Returns the column qualifier for the consumer state column. The qualifier is formed by
  {@code <groupId><instanceId>}.
  @param groupId Group ID of the consumer
  @param instanceId Instance ID of the consumer
  @return A new byte[] which is the column qualifier.