[6.x] Replace system status with maintenance mode

[riasvdv]

Description

Completely replace Craft system status with Laravel maintenance mode. We already partly had this before but we still had the system.live status as well, this completely removes system.live in favor of purely Laravel's maintenance mode.

I've tried to do this without needing to override Laravel's default middleware, but our logic was a bit too specific for this. Replacing the built-in middleware is very rare to do in a Laravel project, so running into an issue with a host app replacing it won't happen often, if at all.

I've also audited all 5.x routes that were allowed when the system was offline, which surfaced a few I missed before.

Adds Route::allowDuringMaintenance() to the route registration, so allowing routes is more straightforward and doesn't separate the excluding (which was in RouteServiceProvider before) from the route registration. The middleware now gathers all routes with that exclusion metadata.

This uses Laravel's new route metadata feature so the Laravel requirement has bumped to 13.17

[linear-code]

CMS-162

[github-actions]

📚 Storybook previews

@craftcms/ui — open Storybook

Changed components:

• Controls/Combobox
• Controls/Input
• Controls/Input Color
• Controls/Input Password
• Controls/Select

resources/js — open Storybook

No changed components detected in this Storybook.