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?

Examine la logique de mise en page sans sidebar dans le composant Page ainsi que le comportement introduit par la pull request #11760. Suivez la manière dont sont gérées les props de sidebar omises, falsey et explicitement définies à null, puis vérifiez que la classe de modification est appliquée dans les cas prévus sans perturber les consommateurs existants.