[Meta] [New docs] Port dynamic documentation pages to docusaurus

[tkajtoch]

Summary

All of the existing dynamic documentation pages, like Customizing themes, must be ported to docusaurus and be available on the new documentation site.

Acceptance Criteria

• The pages are ported to docusaurus and work the same way they do on the current documentation site

### Pages to port to docusaurus
- [ ] [Typography](https://eui.elastic.co/#/theming/typography/values)
- [ ] [Customizing themes](https://eui.elastic.co/#/theming/customizing-themes)
- [ ] [Colors](https://eui.elastic.co/#/theming/colors/contrast)

The list above may expand over time.