Add border-radius tokens about catalog

[prichter]

@Teddarific - can you please elaborate a little more, and assign this to me? A user story might help me with context... Would this potentially, for example, be a display block under the color shades showing the radius for different variations, and a separate edit modal to allow adjusting these values?

[prichter]

Maybe like this (pretending the radii are different sizes)?

Conceptual editing sketch (ignore layout / format):

[alexdanilowicz]

@prichter , you're on the right track. We need to think about it more ourselves, so appreciate you creating a mockup. Will think about it some more.

I think it would be a separate section, like how we just added "Typography". And the section would be called Spacing.

Need to think some more. cc @Teddarific

[Teddarific]

Hey @prichter! Love the mock-ups — going to put this one on hold for now. We want to really nail the experience down for colors, so that once we expand, we can build ontop of a great base.

If you want to put up an initial PR with the functionality, happy to merge it in without the UI, that would be a great help!

[prichter]

@Teddarific this was just a wireframe - if I get some time I might knock up a few bits of the functionality.