[LG-4631] fix 500 page crash when required prop is deselected

[stephl3]

LG-4631

In the live example pages, when a knob uses a Select to set the prop value, allowDeselect={true} by default. However, the prop value of a deselected option is "" which in some cases will throw an error and crash the page. Specifically for the Code component, deselecting the language prop would set language="" which is an invalid prop.

This change will set allowDeselect={false} for all knobs with control type of 'radio'. For props like language that cannot be deselected, the appropriate storybook control in the storybook file must be set to type: 'radio'.

in *.stories.tsx

propName: {
  options: Object.values(OptionNames),
  control: { type: 'radio' },
}