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?

Revisa la lógica del diseño sin sidebar en el componente Page y el comportamiento introducido por el pull request #11760. Rastrea cómo se gestionan las props de sidebar omitidas, falsey y establecidas explícitamente en null, y después verifica que la clase modificadora se aplique en los casos previstos sin romper los consumidores existentes.