Add cockpit for global refetch

[marvinruder]

Describe the solution you’d like
A dashboard allowing for fetching all stocks from a provider and showing the progress of these fetches using a progress bar.

Describe alternatives you’ve considered
OpenAPI dashboard or curl. No progress shown and bad usability.

[marvinruder]

Ideas:

• /progress API endpoint, which is called every second either after button is pressed or while something is still in progress (or Websocket).
• Progress is stored in global variable in fetch controller per data provider.
• Button to cockpit in header of stock list page