Support insert into in offline mode to append offline data

Now `insert into` works for online mode and we can not insert data into offline storage.

It would be better to support in offline mode by using TaskManager or simply append HDFS files.

Look at how `insert into` works in online mode, then examine the TaskManager and HDFS file handling for offline storage. The goal is to append data to offline storage, likely by modifying the insert logic to work with HDFS files. Check existing tests for insert operations to understand the expected behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.