Add option to have an upload only mode in /e/ Sync feature
Summary
Add the ability to select if data has to be downloaded on the device storage, or just uploaded on the /e/ Cloud user account (like a virtual drive, or Google Photos, for exemple)
This feature concerns
Description
Who will use the new feature?
Users with low capacity storage and users with a lot of data.
What is the target of the new feature for this user?
User could decide which data he wants to sync in the cloud, and which he wants to sync on his device.
Why this user would like to use this feature?
Keep its device's storage empty, and still access data.
Examples
Access data in the cloud through apps and not on the device storage. For exemple, I could access my photos in the Gallery app, without having them stored on the device (which would fill its storage pretty quickly, as I have 60Gb of pictures).
## Reflection
Based on this issue about WHAT to sync : #1358 I think it would be useful to have a choice of HOW to sync.