Is your feature request related to a problem? Please describe.

The current file structure of registration attachments export from the registration list is problematic when the conference manager wants to store the files somewhere else and still keep track of the registrant who uploaded them.

The export keeps the uploaded files in a nested structure like such:

./
├── Abensarz_Krzysztof_33/
│  └── File_upload_1220987_KHAbensarz.pdf
├── Camacho_Ninho_Victor_30/
│  └── File_upload_1220987_Abstract-PaE-_Electrodynamics.pdf
├── Sabenso_Gabriel_23/
│  └── File_upload_1220987_Abstract_G.Sabenso.pdf
└── Piotr_Edgar_26/
   └── File_upload_1220987_abstract_PE.pdf

The main problems that conferences manager find are: 1) the actual file has no reference to the submitter, requiring them to manually edit it and 2) they need to go into each subfolder to copy the file out.

Describe the solution you'd like

At the very least, every file should have a reference to the registrant:

./
├── Abensarz_Krzysztof_33/
│  └── Abensarz_Krzysztof_33_File_upload_1220987_KHAbensarz.pdf
├── Camacho_Ninho_Victor_30/
│  └── Abensarz_Krzysztof_33_File_upload_1220987_Abstract-PaE-_Electrodynamics.pdf
├── Sabenso_Gabriel_23/
│  └── Abensarz_Krzysztof_33_File_upload_1220987_Abstract_G.Sabenso.pdf
└── Piotr_Edgar_26/
   └── Abensarz_Krzysztof_33_File_upload_1220987_abstract_PE.pdf

A flat file structure like such would resolve both problems:

./
├── Abensarz_Krzysztof_33_File_upload_1220987_KHAbensarz.pdf
├── Camacho_Ninho_Victor_30_File_upload_1220987_Abstract-PaE-_Electrodynamics.pdf
├── Sabenso_Gabriel_23_File_upload_1220987_Abstract_G.Sabenso.pdf
└── Piotr_Edgar_26_File_upload_1220987_abstract_PE.pdf

Describe alternatives you've considered

When to export with a flat file structure? I can imagine several options:

1. Always. This may not be ideal for registration forms with multiple file uploads or when conference managers want each registrant to have a dedicated folder.
2. Only when single file uploaded. This may not be ideal if the conference manager wants to have a flat structure even when there are multiple files uploaded.
3. When selected explicitly. This would be the ideal solution, as it allows the conference manager select when to have a nested or a flat file structure.

One option to implement 3. would be via a dialog but this seems like an overkill for a single export export. Better than this, I would propose adding a new entry in the actions dropdown button as shown below.