Move auto-update of Supervisor components after startup

Description

Supervisor today auto-updates itself as well as all plug-ins to the latest version before continuing update. This has several downsides:

• Startup is slowed down: This is especially problematic for first time users, the landing page might be reachable quite a bit later, especially if Internet connectivity is slow
• Quite some ordering requirements: The updater which fetches version information must load early enough for the update information to be present. This turned out tricky when working on DNS loading/reloading, since Supervisor itself uses the pulg-in DNS - leaving us in a chicken/egg situation.
• During first time setup, if updating Supervisor or plug-ins fail there is no (or delayed) user feedback (since landing page loads later). Related to that, if Supervisor updates fail the Core update is still run (see #6762).

The only downside updating Supervisor/plug-ins after startup is that there might be intermittent service interruption for the system (e.g. plug-in DNS restart or Supervisor restart). Ideally we make sure that the updates are only run after the system completed startup entirely and is in a settled state.

Additional context

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