Add support for Dropbox Transfer

[elmimmo]

It would be nice to be able to create Dropbox Transfer links for “files you don’t need to collaborate on”. The official macOS client provides a Finder contextual menu command for that.

[samschott]

I was not aware of Dropbox Transfer links before and am not quite sure how they differ from shared links that restrict permissions to viewing and downloading. Maybe that the download starts directly when clicking the link instead of viewing the file first and then downloading?

In any case, the public API does not seem to provide separate endpoints for Transfer links, only for regular shared links. I can however add support to set edit vs view / download permissions on links in the CLI.

So far, I've also shied away from file manager integration in the GUI because this tends to be very platform-specific and would open a can of worms on Linux.