RadioGroup - make legend optional

[larserbach]

In Figma the legend isn't optional yet. The developed component already has an optional legend.
The current layout must be changed, because if the legend is hidden, there remains an undesired top padding on the RadioStack.

Design tasks:

• make the visibility of the legend a boolean prop
• remove token from Radio Stack, or set to zero paddingTop: "Forms.RadioGroup.SM.RadioStack.PaddingTop";
• add wrapper for legend
• add bottom padding for legend wrapper
• document changes on this ticket

Dev tasks:

• create wrapper for legend
• apply tokens provided by des
• remove token if applicable

[DenizSaganak]

Continuing with the ticket Radio Group - add global caption/hint improvements #402

[larserbach]

Design is done
Branch
PR

[DenizSaganak]

Dev is done
PR: #453

[thrbnhrtmnn]

We looked at the component and the padding was moved to the legend in the code, but we could not verify if everything is done, as design is not updated yet.

[DenizSaganak]

Dev is done
PR: #591

[thrbnhrtmnn]

After merge this task can be closed as done. But we will wait for the tokens & git ignore topic to be resolved before doing it.