[Improvement] Change default `HADOOP_USER_NAME` from `datastrato` to `anonymous`

### What would you like to be improved?

The default user passed from API and frontend is `anonymous` if the user is unknown, however, the user used in HDFS and related test is `datastrato`(Hive docker image) , so we need to change them into the same value.

### How should we improve?

_No response_

Search the repository for HADOOP_USER_NAME, the datastrato default, and HDFS-related tests. Update the relevant default and test configuration so unknown users consistently use anonymous, then run the affected HDFS and related tests to verify the change.

Written by the indexing model from the issue text.