get rid of the local cloud cache folder (or move it to SD)

### How to use GitHub

* Please use the 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to show that you are interested into the same feature.
* Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
* Subscribe to receive notifications on status change and new comments.

**Is your feature request related to a problem? Please describe.**
I once found out that nextcloud uses a local cache folder for the cloud files.
I use nextcloud as a backup solution for the (usually large) media files on my phone, so to keep a local cache of the synched files is frustrating, cos it fills up my phone, doubling the space needed for the files in the cloud.

**Describe the solution you'd like**
A possibility to move this cache folder to the SD (at least) would be nice, better yet, just get rid of it. The files are already in two places, locally and the cloud, so why cache them again?

**Describe alternatives you've considered**
If there would be a way to use a deduplication FS on the phone, it wouldn't be such a big deal, but I don't suppose that is an option on android..

**Additional context**
See also my other feature request to archive files (delete them locally) after some specified time.
https://github.com/nextcloud/android/issues/12568