code: public TableKeysAndAttributes addHashOnlyPrimaryKey(
              String hashKeyName, Object hashKeyValue) {
          this.addPrimaryKey(new PrimaryKey(hashKeyName, hashKeyValue));
          return this;
      }
docs: Adds a hash-only primary key to be included in the batch get-item
  operation.
  
  @param hashKeyName name of the hash key attribute name
  @param hashKeyValue name of the hash key value
  @return the current instance for method chaining purposes