Page - update logic to apply sidebar-less layout

Describe the enhancement or change
Followup to https://github.com/patternfly/patternfly-react/pull/11760 where we apply logic to apply a modifier class for sidebar-less layout if sidebar={null} (tldr reason being to avoid breaking consumers who may rely on sidebar being explicitly undefined, but want to keep the layout as-is).

We want to update the logic in the next breaking change so that omitting the sidebar prop (or it otherwise being falsey) will apply this modifier class instead of having to explicitly pass null to the prop.

Is this request originating from a Red Hat product team? If so, which ones and is there any sort of deadline for this enhancement?

Any other information?

Esamina la logica del layout senza sidebar nel componente Page e il comportamento introdotto dalla pull request #11760. Traccia come vengono gestite le props della sidebar omesse, falsey ed esplicitamente impostate su null, quindi verifica che la classe modificatrice venga applicata nei casi previsti senza interrompere i consumer esistenti.