[design-system] Replace custom size type with tailwind classes

[JammingBen]

We currently define a custom SizeType in the design-system (https://github.com/opencloud-eu/web/blob/main/packages/design-system/src/helpers/types.ts#L81), that we use in several components. This comes from a time where we didn't have Tailwind. Now that we're using it, it would be better for those components to use actual Tailwind class names (e.g. size-4, size-6, etc.). This would nice because:

• Compliance with Tailwind, less custom logic
• More flexibility for the consumer of the components

For reference, the OcIcon component already as a new property sizeClass that takes Tailwind classes.

Removing SizeType will be a breaking change.