Choose file name for scanned documents

### Is your feature request related to a problem? Please describe.
Currently after scanning a document, the scanned document is placed in the root nextcloud directory with a timestamp of the filename. This is fine for a quick one-off scan, but for any kind of regular scanning it becomes tedious to find the file after scanning, rename it, and then move it to the proper directory.

### Describe the solution you'd like
It would be nice to be be able to choose a name and default directory to contain scans.

### Describe alternatives you've considered
Currently i scan the document, save it, then look in the root nextcloud directory for the file, then rename it, then move it to the proper destination.

### Additional context
I came from the iOS app which has a nice [implementation](https://nextcloud.com/blog/take-your-home-office-anywhere-with-nextcloud-coherence-for-ios-text-recognition-for-scanned-files-and-more/):