Notifications must support language-aware content

[olebhansen]

BR asks if/how we can help support this, to meet legal requirements: https://lovdata.no/dokument/NLO/lov/1980-04-11-5

This also has cascading implications in:

1. Profile/mastering of language settings (where is this information originating from, and under what circumastances. KRR has some settings, but an App, who can also trigger a notification, may have other/additional "local" preferences).
2. How to manage templates efficiently (if opting for a template-approach like Altinn2)
3. Should probably look similar to Correspondence, who will also have to support the same, both in their own capacity, and also as an upstream user of Notifications.