Button border radius can't be changed through token

[fleven-kds]

The button component utilizes the --c-button-border-radius token, which is initially set to --ks-border-radius-control. In the DSA theme, the button is designed to have a pill shape. However, not all control items should adopt this pill shape, so the component token is specifically overridden to --ks-border-radius-pill.

The issue here is that once the component token is overridden, it loses its connection to the original design token. As a result, it can no longer be modified through theming. This means that any changes made to the design token will not reflect on the button component because the link between them has been severed by the override.

[julrich]

We should add --ks-border-radius-button to specifically control button radii here.