[2.x] Responsive widget arrangement

[danharrin]

filamentphp/filament#3628 filamentphp/filament#3816

Dennis:

The docs state that widgets can be any number from 1-12 cols wide, but currently it's fixed to 2 cols. I think we should go with a common 12-col-grid as the doc states.

https://filamentphp.com/docs/2.x/admin/dashboard/getting-started#customizing-widget-width