Give good overview of tasks needed for v2 migration

Until then, the Plan de migration v2 was a single post referencing different subjects. I aim to refactor that in more concrete action task to be displayed in a kanban. The goal is to give a broad but pragmatic overview of the steps needed to get migration ready.

In this topic, we can discuss about a way of organizing the board so that people understand better its content.

We still have to detail blocking tasks, not only technical ones (code) but also community ones (smith training, new rules explanation…).