As a sysadmin, I want to see the progress of the intial historical insights import

As part of the historical insights import from #160 (closed) , I want to have some visual indication that the process is running.

Requirements:

• Such indication should be visible in the registration page or in the observatory, while the process is running.
• The exception of the login page happens because the user can see such page only when the registration has finished, meaning that they've already seen such progress happening either in the registration page or in the observatory.
• In case it ends before the user finishes the registration page, it should show, during the registration, that the importing is done.
• The progress should not block any user's action and explicitly indicate it's happening in the background, without requesting user's interaction.