Fix presets containing `picsum.photos` links because of Storybook examples

[julrich]

Like this here: https://github.com/kickstartDS/ds-agency-premium/blob/main/src/components/hero/hero.schema.json#L70-L72
Referencing this: https://github.com/kickstartDS/content/blob/next/source/visual/visual.schema.json#L58

Because Storybook uses those examples to fill in unused values, those also end up in our presets for Storyblok. In turn, they get added into components like the Hero component, where they can trigger weird behavior (e.g. see: kickstartDS#5).