Add cli parameter to download files directory recursively without opening

### Description

**This feature request is focused on Linux. I cannot judge whether it is also relevant for the MacOS and Windows clients.**

When using virtual files (suffix mode), users should be able to only download individual files as well as whole directories locally without opening them.

### Use case

- Requirement to have a whole directory available locally (e.g. files depending on local directory structure, e.g. images in an presentation)
- Avoiding unwanted side effects that might occur when opening a file in the associated application (e.g. scripts, binaries)

### Considerations

On Linux, the downloading of virtual files is is currently implemented by adding a mime type for the "*.nextcloud" file pattern and associating it with the nextcloud application which is then called like this when double clicking a `.nextcloud` file: `nextcloud myfile.txt.nextcloud`.

It will then download the file, remove the virtual one and open the downloaded file with whatever app the OS seems fit for the file type.

If the nextcloud desktop client had a flag to only download a file or directory (recursively), e.g. `nextcloud --download-and-quit myfile.txt.nextcloud`, it would be trivial to integrate this into the context menu of file managers.