add grub support

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

convert_options.go

@@ -22,6 +22,7 @@ type convertOptions struct {
 	output         string
 	cmdLineExtra   string
 	networkManager NetworkManager
+	bootLoader     string
 	raw            bool
 
 	splitBoot bool
@@ -62,6 +63,12 @@ func WithNetworkManager(networkManager NetworkManager) ConvertOption {
 	}
 }
 
+func WithBootLoader(bootLoader string) ConvertOption {
+	return func(o *convertOptions) {
+		o.bootLoader = bootLoader
+	}
+}
+
 func WithRaw(raw bool) ConvertOption {
 	return func(o *convertOptions) {
 		o.raw = raw