add a preview note for all non-bootstrap commands

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

cmd/flux/create_alertprovider.go

@@ -37,7 +37,7 @@ import (
 var createAlertProviderCmd = &cobra.Command{
 	Use:   "alert-provider [name]",
 	Short: "Create or update a Provider resource",
-	Long:  "The create alert-provider command generates a Provider resource.",
+	Long:  withPreviewNote(`The create alert-provider command generates a Provider resource.`),
 	Example: `  # Create a Provider for a Slack channel
   flux create alert-provider slack \
   --type slack \