bundle: add test bundling changeset in the "archived" phase Having this test highlight that phase bundling above secret is significantly broken. Fixes coming in the next changesets.

bundle: introduce a "v3" spec This is a small update from "v2", we use the freshly out of experimental changelog version "03' format (alignment with bundle version is a coincidence) and we now bundle phases by default. We shall use v3 as the default bundle type later, when changegroup version '03' is a bit more established