containerd: update config to v2 format
containerd: update config to v2 format

v2 format has to be declared explicitly to avoid deprecation warning. v2 format
uses long form plugin names e.g. "io.containerd.snapshotter.v1.btrfs" instead
of "btrfs"

Signed-off-by: Aidan Oldershaw <30ef7a6e0d016bc846f26d89dacbd23aceded206@pivotal.io>
Co-authored-by: Muntasir Chowdhury <3af480f42ae632f8ec7bb4ce9ac5df283cd495d6@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse