To avoid packages specified in a blueprint from conflicting with exclude
lists, we depsolve blueprint packages separately and pass them into the
Manifest generator under the new "blueprint" package set key.
This approach has the added benefit that dependencies of packages
specified in the blueprint are not subject to exclusion in addition to
the explicitly named packages.
The OS pipeline which installs the packages for the base system merges
the two package sets before running the RPM stage. The signature of the
function is changed to explicitly require blueprint packages be
specified (though `nil` or empty slice is valid).
The kernel selection test is adapted to merge the package sets before
counting kernel package.
Adaptation of changes in
https://github.com/osbuild/osbuild-composer/pull/1349
cba720e63f