[Assets][Files] Files and subfolders are not include when exporting a folder

[natshabat]

Name and Version

[FE]0.15.0-rc [BE]0.15.0-rc

What steps will reproduce the bug?

BE support is required. Related to FE bug: epam/ai-dial-admin-frontend#2427

Go to Assets → Files.
Select a folder that contains:
• Files directly inside it
• One or more subfolders (with files inside them).
Click Export.
Open the exported archive.

What is the expected behavior?

The export should include: All files inside the selected folder; All nested subfolders; All files inside subfolders.

What do you see instead?

• Only the selected folder is exported.
• Files inside the folder are missing.
• Subfolders and their files are not included in the export.

Additional information

No response