Code review comment for ~smoser/maas:cleanup/render-curtin-config-internally

I think the general idea is great, but we need to think about the upgrade path.

What happens if they made changes to the sections that you have not made internal? Will there changes override the internal changes?

Also this is more of a future thing, but I would prefer to see the templates move into the database with an API, because at the moment with HA, these are a problem.