Issue #3260368 by phenaproxima: Improve the UX for updates that require database changes

automatic_updates.routing.yml

src/BatchProcessor.php

src/Controller/UpdateController.php

src/Form/UpdateReady.php

src/Validator/StagedDatabaseUpdateValidator.php

...utomatic_updates_test/automatic_updates_test.services.yml

...atic_updates_test/src/Controller/TestUpdateController.php

...dules/automatic_updates_test/src/Form/TestUpdateReady.php

...es/automatic_updates_test/src/Routing/RouteSubscriber.php

tests/src/Functional/AutomaticUpdatesFunctionalTestBase.php

tests/src/Functional/UpdaterFormTest.php