Allow drag and drop in a notebook to upload to a particular storage

[josevalim]

Currently it is always an attachment, but we could choose "Upload to storage and store link".

[jonatanklosko]

This can already be achieved by drag-and-dropping into the file navigator here:

When dropping a file in the notebook, we show "From upload" tab with the file selected. We could add a radio, but then we need to conditionally show the navigator, so the user can select the storage and path.

I think ideally we should avoid duplicated workflows, because the "Add file" modal already has a bunch of variants. Instead, we could show a tip like this:

WDYT?

[josevalim]

Sounds great! I would just say:

This will upload the file as an attachment in the notebook /files directory. If you want to upload it to a file storage instead, choose "From storage", then drag and drop the file to the desired storage and directory.