@Override
  public String toString() {
    return String.format("%s%s%s", checkpointId, SEPARATOR, changelogOffset);
  }
WARNING: Do not change the toString() representation. It is used for serde'ing the store changelog offsets
as part of task checkpoints, in conjunction with {@link #fromString(String)}.
@return the String representation of this {@link KafkaChangelogSSPOffset}
samza-core/src/main/java/org/apache/samza/checkpoint/kafka/KafkaChangelogSSPOffset.java