Documentation of Send notifications User guide

[annerisbakk]

Description

User guide communication the app owners responsibilities and guidelines for using Altinn Notifications should be documented.
We have some existing documentation, but this should be updated and moved to docs.

Existing doc: https://www.altinndigital.no/produkter/varsling/, https://altinn.github.io/docs/utviklingsguider/varsling/

This is not a task that needs to be completed by a developer on team core. Hoping product owner or another part of the business. Legal coaches etc. could support us in this delivery.

Documentation should be placed here User guide

[olebhansen]

Goal: Move existing doc to new structure.

Need legal opinion on various topics ("what is a notification", guidelines for SMS content).