Get Colours, Typography and Spacing pages using tokens

[amyhupe]

What

Update Nature Colours, Typography and Spacing pages to consume design tokens.

Why

To make the documentation easier to maintain and ensure it's in sync with the source of truth (code).

Done when

• [ ] Gather examples of tokens docs
• [ ] Elements team reviews examples and decides what's needed for Springer Nature
• [ ] Update pages as agreed to use tokens

[sturobson]

We can close this as it's part of 'the work' involved in the SRS