Theme Next - Heading typography option Amplitude

[origami-z]

### Tasks
- [ ] Add new foundation typography headings token, default to Open Sans
- [ ] Point h1/2/3/4, display 1/2/3 to new heading token
- [ ] Add new palette layer types (heading / body), point text characteristics to palette instead of foundation
- [ ] Add new amplitude typography foundation variable
- [ ] Add new amplitude font-face declaration file
- [ ] Upload Amplitude font for storybook to use (but not distribute through npm package for licensing issue)
- [ ] Add additional theme-next in palette point heading to amplitude
- [ ] Add additional option to Unstable SaltProvider, to switch between 2 font options
- [ ] Add new toggle to storybook toolbar to demo
- [ ] ??? Does font weight needs remapping? Or let browser choose?
- [ ] Update theme next doc with relevant information