Move the subscription options from distro to its own package.
Now we can import the manifest package into the distro package (instead
of the other way around) so we can work with the manifest.Manifest type
in distro.
The post install script customises the selinux policy, but is gated on
`selinuxenabled`, which will fail inside the buildroot container.
As a result it's never executed.
There are 3 different ways for subscriptions to be setup, test the
pipeline to make sure it includes the correct commands, and check the
package set chain to make sure it includes the packages needed to
support the selected subscription mode.
