Add DO NOT EDIT warn to bootstrap sync manifests

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

pkg/manifestgen/manifest.go

@@ -24,6 +24,8 @@ import (
 	securejoin "github.com/cyphar/filepath-securejoin"
 )
 
+const GenWarning = "# This manifest was generated by flux bootstrap. DO NOT EDIT."
+
 // Manifest holds the data of a multi-doc YAML
 type Manifest struct {
 	// Relative path to the YAML file