Distinguish between "private" ("test", pre-publication, etc.) versus "public" data sets in the system

[RichardBruskiewich]

At this moment (Sept 21, 2021), all data sets uploaded to the KGE archive are immediately visible and available for downloading after they are fully uploaded.

For whatever reason, clients uploading data may have "private" data sets which they consider "tests" of the system or datsets which they wish to keep under escrow until a certain time. In either case, such datasets should only be visible to the client uploading them, until which time such a client tells the system that they should be "public", hence, visible for downloading by all registered users of the system.