Add Categorical color palette

[pseys]

### Tasks
- [x] Define categorical color palette
- [ ] Update Figma
- [ ] Update code (@origami-z)

[bhoppers2008]

18th Jan meeting notes:

• Will be known as 'Category' palette.
• Will be part of Salt Theming release (formally 2.0).
• Full set of colours will be available at Foundations, with 3 levels per colour, per mode.
• Will be mapped to the palette layer (not characteristic).
• Palette layer naming will be colour agnostic (ie., --cat-1, --cat-2, --cat-3, etc).
• Levels will be defined as --weak, --default and --strong.

@pseys @dplsek @origami-z @joshwooding

[pseys]

• Token structure and relationship mapped in Figma.
• In the process of adding colors to variables-driven library

[origami-z]

Reopen until characteristics token is in