Delete whole local file cache

### Is your feature request related to a problem? Please describe.
I'm missing a feature for deleting the whole file cache of the Android app. When working with many files, these often needs to get downloaded in the app. These downloaded files remain in the local cache.
In order to clear the cache, you have to navigate to "on this device" in the app's menu and delete all folders shown (be careful that you only delete the cache and not the files in the cloud).

### Describe the solution you'd like
The app for iOS has a feature in its settings to delete the whole file cache of the app by only one tap.
I would love to see such a feature for the Android app.

### Describe alternatives you've considered
As described above, delete all cached folders from "on this device".