Fix or retire legacy notifications in the Updater to avoid constant updater notifications if the Notifications app is disabled

How to use GitHub

• Please use the 👍 reaction to show that you are interested into the same feature.
• Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
• Subscribe to receive notifications on status change and new comments.

Is your feature request related to a problem? Please describe.
Yes, when there is a brand new update that I can't update to, because some of my extensions aren't yet compatible with it, I keep getting annoying popups that are telling me I should update to new version every single time I load any page, or refresh it. I need to disable this.

Describe the solution you'd like
I want to be able to disable all those annoying update notifications.

Describe alternatives you've considered
I was looking through the admin configuration, couldn't see any option to disable it.

Additional context

Start by tracing the Updater's legacy notification path and how it behaves when the Notifications app is disabled. The issue names no files or tests, so first locate the Updater entry point and related Notifications app handling. Done means the repeated updater notifications no longer appear in that state, with the intended supported behavior agreed.