QR code to share a link, in situations where you don't exchange contact-details

### Is your feature request related to a problem? Please describe.
Usecase:
I often use Nextcloud to share files with people I see only once.
Often we don't even exchange phonenumbers/contact details, otherwise I would have used Whatsapp.

Examples: I meet a photographer who agrees to share some specific photos with me. Or I take a street portrait of a stranger and of course they would like a copy.

My ideal situation is this:
- I can create a shared folder, right there and then on my phone
- Instead of using Whatsapp (which requires the exchange of contact details), I show them a QR code with a direct link to the folder.
- They scan it and keep it
- At home I upload the data in the folder and they can access it
- or they can use the link to upload data which I can view later