refactor: migrate color palettes to grid layouts

This migrates the color palettes away from rows and cols in favor of grid layouts. The primary goal here is to rely on GitLab UI utils instead of custom ones.

As part of these changes, the spacing between palettes is being slightly revisited and the data visualization layout is aligned with the foundations one.

	Before	After
Foundations > Color	https://design.gitlab.com/product-foundations/colors	https://4456656-review-color-pale-e7ltzf.design-staging.gitlab.com/product-foundations/colors
Data visualization > Color	https://design.gitlab.com/data-visualization/color	https://4456656-review-color-pale-e7ltzf.design-staging.gitlab.com/data-visualization/color

Re #372 (closed)