Promote image CLI commands to stable

Remove experimental status from flux image commands in preparation
for GA release of image automation APIs.

Partial fix for #5411

Signed-off-by: Daniel Guns <danbguns@gmail.com>

cmd/flux/get_image_update.go

@@ -32,7 +32,7 @@ import (
 var getImageUpdateCmd = &cobra.Command{
 	Use:   "update",
 	Short: "Get ImageUpdateAutomation status",
-	Long:  withPreviewNote("The get image update command prints the status of ImageUpdateAutomation objects."),
+	Long:  "The get image update command prints the status of ImageUpdateAutomation objects.",
 	Example: `  # List all image update automation object and their status
   flux get image update