Add maps for all colors, document how to extend color utilities (#32319)

Add maps for all colors, document how to extend color utilities (#32319)

* Add maps for all colors, document how to extend color utilities

* Updates to make this more functional for v5

- Moves color maps into _variables.scss for now (felt weird to split them out when the variables are there)
- Adds a new function, map-merge-multiple(), and updates docs that reference combo-map
- Updates code snippet and docs guidance about how to extend the color utils to handle this

* Update site/content/docs/5.0/customize/color.md

Co-authored-by: Gaël Poupard <ffoodd@users.noreply.github.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>