main: add new --registrations options

This new flag allows to add a file with registration data. This
is meant to eventually hold all sort of registrations like
ansible or satelite but initially only contains the redhat
subscription. Currently only JSON is supported.

It looks like:
```json:
{
  "redhat": {
    "subscription": {
      "activation_key": "ak_123",
      "organization": "org_123",
      "server_url": "server_url_123",
      "base_url": "base_url_123",
      "insights": true,
      "rhc": true,
      "proxy": "proxy_123"
    }
  }
}
```

This is not part of the blueprint (today) because its more
ephemeral than the things we usually put into the blueprint.

This allows us to build images that are immediately registered. It
also keeps our options open in the future. If we move to a new
blueprint format where we support multiple blueprints and also
ephemeral data like this the "registrations" flag just becomes an
alias for "--blueprint".

cmd/image-builder/main_test.go

@@ -2,6 +2,7 @@ package main_test
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -18,6 +19,9 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/osbuild/images/pkg/distro"
+	"github.com/osbuild/images/pkg/dnfjson"
+	"github.com/osbuild/images/pkg/rpmmd"
 	testrepos "github.com/osbuild/images/test/data/repositories"
 
 	main "github.com/osbuild/image-builder-cli/cmd/image-builder"
@@ -948,3 +952,81 @@ func TestBasenameFor(t *testing.T) {
 		assert.Equal(t, tc.expected, main.BasenameFor(res, tc.basename))
 	}
 }
+
+// XXX: move into as manifestgen.FakeDepsolve
+func fakeDepsolve(cacheDir string, depsolveWarningsOutput io.Writer, packageSets map[string][]rpmmd.PackageSet, d distro.Distro, arch string) (map[string]dnfjson.DepsolveResult, error) {
+	depsolvedSets := make(map[string]dnfjson.DepsolveResult)
+
+	for name, pkgSetChain := range packageSets {
+		specSet := make([]rpmmd.PackageSpec, 0)
+		for _, pkgSet := range pkgSetChain {
+			include := pkgSet.Include
+			slices.Sort(include)
+			for _, pkgName := range include {
+				checksum := fmt.Sprintf("%x", sha256.Sum256([]byte(pkgName)))
+				spec := rpmmd.PackageSpec{
+					Name:     pkgName,
+					Checksum: "sha256:" + checksum,
+				}
+				specSet = append(specSet, spec)
+			}
+
+			depsolvedSets[name] = dnfjson.DepsolveResult{
+				Packages: specSet,
+				Repos:    pkgSet.Repositories,
+			}
+		}
+	}
+
+	return depsolvedSets, nil
+}
+
+func TestManifestIntegrationWithRegistrations(t *testing.T) {
+	restore := main.MockManifestgenDepsolver(fakeDepsolve)
+	defer restore()
+
+	restore = main.MockNewRepoRegistry(testrepos.New)
+	defer restore()
+
+	// XXX: only "proxy_123", "server_url_123" are actually observable
+	// in the manifest(?)
+	fakeRegContent := `{
+  "redhat": {
+    "subscription": {
+      "activation_key": "ak_123",
+      "organization": "org_123",
+      "server_url": "server_url_123",
+      "base_url": "base_url_123",
+      "insights": true,
+      "rhc": true,
+      "proxy": "proxy_123"
+    }
+  }
+}`
+	fakeRegistrationsPath := filepath.Join(t.TempDir(), "registrations.json")
+	err := os.WriteFile(fakeRegistrationsPath, []byte(fakeRegContent), 0644)
+	assert.NoError(t, err)
+
+	// XXX: fake the depsolving or we will need full support for
+	// subscripbed hosts in the tests
+	restore = main.MockOsArgs([]string{
+		"manifest",
+		"qcow2",
+		"--arch=x86_64",
+		"--distro=rhel-9.6",
+		"--registrations", fakeRegistrationsPath,
+	})
+	defer restore()
+
+	var fakeStdout bytes.Buffer
+	restore = main.MockOsStdout(&fakeStdout)
+	defer restore()
+
+	err = main.Run()
+	assert.NoError(t, err)
+
+	// XXX: manifesttest really needs to grow more helpers
+	assert.Contains(t, fakeStdout.String(), `{"type":"org.osbuild.insights-client.config","options":{"proxy":"proxy_123"}}`)
+	assert.Contains(t, fakeStdout.String(), `"type":"org.osbuild.systemd.unit.create","options":{"filename":"osbuild-subscription-register.service"`)
+	assert.Contains(t, fakeStdout.String(), `server_url_123`)
+}