Minimum screen width support

[mrosvik]

We should add guidelines or considerations regarding the minimum screen width we should support. Some components, such as the modal, do not fit properly on a 320px wide screen but work fine on 375px and above.
Example: Link to Chromatic Test.

This raises the question of whether we need to establish a minimum screen width for consistent functionality across devices.

[mrosvik]

Møte 9.okt: Vi er enige om at vi bør støtte 320. Når vi støtter 320 vet vi også at vi er innenfor kravene på 400% zoom.

Relatert til sizing-issue: #2508