Introduce a new view, model and controllers pair to enable Ubuntu
Advantage from Subiquity. For now, we expect the user to input an
alphanumeric token and rely on cloud-init to enable the features
associated with the subscription.
This implementation comes with a number of limitations:
* inability to validate the token before first-boot
* inability to check what features are associated with the Ubuntu
Advantage subscription, before first-boot
* the user must input the token directly: there is no mechanism to
deduce the token based on email address and password.
The new screen is placed after the identity scree. The installation
should already be running when the UA screen will be shown to the user.
Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>
Olivier Gayot