This PR closes #49.
It adds the following features:

• Showing a spinner in the references view while uploaded files are being uploaded
• Updating the references view with new references once ingestion is done
• Changing the way references are represented in the editor to use the markdown syntax
• Connecting the suggestion widget to the actual list of references so that typing [ in the editor enables you to insert a reference

Implementation choices:

• One jotai atoms has been created to store references
• When ingestion is running, file uploading is disabled
• This PR uses the Mention extension of TipTap to open the suggestion list when typing [
  • This works for now but the extension is not really customisable and can only be rendered as text, we may have to create our own custom extension if we want to support having a tooltip with information about the reference when hovering it in the editor
• This PR uses react-popper to render the suggestion list
  • The suggestion extension requires a library to position the list
  • Mention comes with tippy but we need a react implementation because jotai atoms are only available in the React world (if we want to avoid having to handle stores)
  • tippyjs/react would be an alternative we can use