[gamut-badge] Use Object prop for gamuts

[LeaVerou]

<gamut-badge> accepts its list of gamuts as either a list of ids, or a list of ids with optional labels, like "srgb, p3, rec2020: P3+, prophoto: PP". That’s exactly what Object props do. When this was written, we didn't have these yet, but now that we do, we should use them, instead of doing it ad hoc.