[Docs]Document clarifying notes about the data lifecycle

[popojk]

Tracking issue

Closes #4683

Why are the changes needed?

1. The Understand How Flyte Handles Data doc is lacking information about deleting raw data in storage service such as s3 and gcs.
2. Some example code in the doc is incorrect. The workflow called a function 'task_read_and_shuffle_file', but the function is not defined in example code.

What changes were proposed in this pull request?

1. Add information about raw data deletion in the doc.
2. Fix example code.

Check all the applicable boxes

• I updated the documentation accordingly.
• All commits are signed-off.

Docs link

https://flyte--5921.org.readthedocs.build/en/5921/user_guide/concepts/main_concepts/data_management.html