void addEntry(Offset offset, StoreKey key) {
    addEntry(offset, key, null);
  }
Adds an entry into the journal with the given {@link Offset}, {@link StoreKey}, and a null crc.
@param offset The {@link Offset} that the key pertains to.
@param key The key that the entry in the journal refers to.
ambry-store/src/main/java/com/github/ambry/store/Journal.java