Design of notification v2 backend

[olebhansen]

Collaborative task. Work in pair to gather/clean existing tasks and create new ones as needed. The goal is to have a plan on how to implement the v2 API of notification.

Have at least one team-wide session on the timeline/dependencies and key design choices/tradeoffs.

End result is a team-wide understanding for what, how and when, so we can move into implementation steps ASAP.