New component: Stepper

[mrosvik]

Related issues or relevant information?

• https://github.com/Altinn/app-frontend-react/issues/97
• https://github.com/Altinn/app-frontend-react/issues/188 (Progress indicator made for "Elevundersøkelsen")

Related research:

• https://www.linkedin.com/posts/vitalyfriedman_ux-design-activity-7127577055029796864-0JVK?utm_source=share&utm_medium=member_ios

Other Stepper components

• Carbon progress-indicator: https://carbondesignsystem.com/components/progress-indicator/usage/
• Carbon progress-bar: https://carbondesignsystem.com/components/progress-bar/usage/
• Gov UK: https://design-system.service.gov.uk/patterns/step-by-step-navigation/
• Fælles designsystem: https://designsystem.dk/komponenter/trinindikator/
• Entur: https://design.entur.org/komponenter/navigasjon/stepper
• Nav: https://aksel.nav.no/komponenter/core/stepper
• Atlassian: https://atlassian.design/components/progress-tracker/examples (See also progress bar and progress indicator)

Specification and requirements

• Add specification and requirements

### Tasks
- [ ] Stepper: Write about specification, requirements and scope in this issue
- [ ] https://github.com/digdir/designsystem/issues/1120
- [ ] https://github.com/digdir/designsystem/issues/1121
- [ ] https://github.com/digdir/designsystem/issues/1122