Allow to select a storage path for each synchronized folder

### Is your feature request related to a problem? Please describe.
By now you are only able to select one Storage Path in the Android App. So all your Data is stored either on the Internal Storage or the SDcard for example. Because of that I'm not able to select different Storage Paths for different Folders.

### Describe the solution you'd like
I woul'd be very happy, if it would be possible to select a the Storage Path for each Folder I'm synchronizing to my Phone. There should still be a default Storage Path. For example i have data that should be on the encrypted Internal Storage like private Things. But there is also Data, that I'd like to store on the SDcard, because there is more space available, for example for Musik.
For example there could be an additional menu entry after "sync" like "sync to custom Folder" where you can select the Path you want to Sync the Data to. In the Desktop App this is already available.

### Describe alternatives you've considered
The current alternative is to manually copy the files to the SDcard.

Thank you for your great work on all Nextcloud code.