cmd: add osbuild-package-sets for printing package sets of an image

Add a new debugging / development tool `osbuild-package-sets` for
printing JSON object with all package sets of a specific distro x arch x
image type combination.

This is useful, since due to the way package sets are implemented in
composer, the actual package set of a vanilla image type is very
difficult to determine just by looking at the code.

Example usage:
`go run cmd/osbuild-package-sets/main.go -distro rhel-90 -arch x86_64
-image qcow2`

cmd/osbuild-package-sets/main.go

@@ -0,0 +1,46 @@
+// Simple tool to dump a JSON object containing all package sets for a specific
+// distro x arch x image type.
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/osbuild/osbuild-composer/internal/blueprint"
+	"github.com/osbuild/osbuild-composer/internal/distroregistry"
+)
+
+func main() {
+	var distroName string
+	var archName string
+	var imageName string
+
+	flag.StringVar(&distroName, "distro", "", "Distribution name")
+	flag.StringVar(&archName, "arch", "", "Architecture name")
+	flag.StringVar(&imageName, "image", "", "Image name")
+	flag.Parse()
+
+	dr := distroregistry.NewDefault()
+
+	distro := dr.GetDistro(distroName)
+	if distro == nil {
+		panic(fmt.Errorf("Distro %q does not exist", distro))
+	}
+
+	arch, err := distro.GetArch(archName)
+	if err != nil {
+		panic(err)
+	}
+
+	image, err := arch.GetImageType(imageName)
+	if err != nil {
+		panic(err)
+	}
+
+	encoder := json.NewEncoder(os.Stdout)
+	encoder.SetIndent("", "  ")
+	pkgset := image.PackageSets(blueprint.Blueprint{})
+	_ = encoder.Encode(pkgset)
+}