Group Export doesn't include uploads directory
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### Summary
Group export export Epic but not any images in the epic.
### Steps to reproduce
1. Create an Epic.
2. Upload an image in the description.
3. Export Group.
4. No image is exported.
### What is the current *bug* behavior?
The Epic is exported but the images are not exported along.
### What is the expected *correct* behavior?
Any images in `/uploads/` should also be exported.
#### Results of GitLab environment info
Verified this in 16.4 but also in older versions.
### Possible fixes
Include the Group uploads directory in the export.
This is a missing feature. We do export uploads for projects [here](https://gitlab.com/gitlab-org/gitlab/-/blob/d530de1fcd93a9fbadf21e4d6b1711ac6935a5bc/app/services/projects/import_export/export_service.rb#L24-30)), but we never exported uploads for groups in file-based Import/Export.
issue