Minor fix on stepper

[DavideMininni-Fincons]

Some minor details to fix:

• the long label does not wrap in vertical. is it ok? didn't find a Figma sketch for it
• found a weird behavior: on the first story, if i clear the input, than set the focus on the first step, moving with right arrow goes to second step (not sure if it's correct). After that i cant get back to the first one.
• refactored a bit the stories, see https://github.com/sbb-design-systems/lyne-components/compare/chore/stepper-stories?expand=1

Originally posted by @DavideMininni-Fincons in https://github.com/sbb-design-systems/lyne-components/pull/2491#pullrequestreview-2101680070