Generate image pull secret at bootstrap

Add an optional flag called `--registry-creds` to the bootstrap
command for generating an image pull secret for container images
stored in private registries.

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

pkg/manifestgen/install/options.go

@@ -26,6 +26,7 @@ type Options struct {
 	ComponentsExtra        []string
 	EventsAddr             string
 	Registry               string
+	RegistryCredential     string
 	ImagePullSecret        string
 	WatchAllNamespaces     bool
 	NetworkPolicy          bool
@@ -46,6 +47,7 @@ func MakeDefaultOptions() Options {
 		ComponentsExtra:        []string{"image-reflector-controller", "image-automation-controller"},
 		EventsAddr:             "",
 		Registry:               "ghcr.io/fluxcd",
+		RegistryCredential:     "",
 		ImagePullSecret:        "",
 		WatchAllNamespaces:     true,
 		NetworkPolicy:          true,

pkg/manifestgen/sourcesecret/sourcesecret.go

@@ -83,7 +83,7 @@ func Generate(options Options) (*manifestgen.Manifest, error) {
 
 	var dockerCfgJson []byte
 	if options.Registry != "" {
-		dockerCfgJson, err = generateDockerConfigJson(options.Registry, options.Username, options.Password)
+		dockerCfgJson, err = GenerateDockerConfigJson(options.Registry, options.Username, options.Password)
 		if err != nil {
 			return nil, fmt.Errorf("failed to generate json for docker config: %w", err)
 		}
@@ -223,7 +223,7 @@ func resourceToString(data []byte) string {
 	return string(data)
 }
 
-func generateDockerConfigJson(url, username, password string) ([]byte, error) {
+func GenerateDockerConfigJson(url, username, password string) ([]byte, error) {
 	cred := fmt.Sprintf("%s:%s", username, password)
 	auth := base64.StdEncoding.EncodeToString([]byte(cred))
 	cfg := DockerConfigJSON{