text: Title: Allow to download all attachments with one click
  Body: ### Proposal
  
  The whistleblower or recipient  may want to download all attachments. 
  
  A button could be provided to download all attachments in a zip or include a check next to each attachment to select those to download.
  
  e.g.
  
  ![image](https://github.com/globaleaks/GlobaLeaks/assets/23368434/a671d9b2-1e99-4b02-b999-f9580ebc0eee)
  
  
  ### Motivation and context
  
  If the number of attachments is large, clicking on the download icon one by one is tedious.
  
  This improves the usability and user experience and makes it easier for the recipients.