WIP: feat: [#2498] Allow drag-n-drop in a notebook to upload to a particular storage

[Liferenko]

This PR is for #2498

TODO:

• add uploaded file's link in a sidebar "Files/references"
• validate radio (when user forgot to choose one of options)
• tests, u know

DoD:

• user can upload a file via drag-n-drop as an attached file into current notebook
• user can upload a file in "global" storage and find their file in a current notebook's "References"

[CLAassistant]

All committers have signed the CLA.

[jonatanklosko]

Closing in favour of #2868.