Each image type now implements BuildPipelines(), which returns a list of
pipeline names that set up the build environment, and
PayloadPipelines(), which returns a list of pipeline names that create
the OS image (all non-build pipeline names).
Older distros that produce v1 manifests should call the distro Fallback
functions to return the common defaults.
A Fallback function for the Exports() method is also added and called by
older distros.
All image types that produce v2 manifests (distros after RHEL 8.4)
should include the information in the image type definition and should
not rely on fallbacks for default values.
Signed-off-by: Achilleas Koutsou <achilleas@koutsou.net>
