imageTypeS2 implements the distro.ImageType interface buts generates a
Manifest matching the new osbuild v2 schema.
Two new image types are added to the rhel84 distro (x84_64 and aarch64)
for generating OCI containers contain an Edge (ostree) commit and, when
run, start a web serer to serve the commit.
The image type uses the new PackageSets map to define packages (and
excludes) for the image. The old methods (Packages() and
BuildPackages()) are implemented for compatibility with the old
workflow.
The image also defines an extra package set for the container that will
serve the package: "httpd" (and its dependencies).
The distro.ImageType interface has a new method: Exports()
It should return a list of names or IDs of artefacts that should be
exported from osbuild when the job is complete.
For the old image types, this is simply set to "assembler".
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