AboutModal - update examples/demos to specify background image source

[mcoker]

core issue - patternfly/patternfly#5530

Core no longer ships a background image for the <BackgroundImage> or <AboutModal> in the CSS. The <BackgroundImage src="..."> is already required in react, so nothing to do there, but the react <AboutModal> examples rely on the background image from core for its default background image (the PF logo). Those examples will likely need an update to add backgroundImageSrc="/assets/images/pfbg-icon.svg". It's the same image path specified in the <BackgroundImage> component examples.

[gitdallas]

Commented some stuff out related to this to update pf core
https://github.com/patternfly/patternfly-react/pull/9108/files