What would be the recommended way to offer a variant/option type filter like we have for taxons? For example, in the demo store's clothing category page, it would be great to have shop by color and shop by size options. Currently, I've implemented a solution that simply duplicates option types to taxons, but since taxons apply to the entire product and option types apply to variants this is a very bad design. I think this might be a commonly needed and implemented feature, and would like to learn from your experience implementing it.