dir2config: support json output

cmd/dkl-dir2config/main.go

@@ -1,10 +1,12 @@
 package main
 
 import (
+	"encoding/json"
 	"flag"
 	"io/fs"
 	"log"
 	"os"
+	"path"
 	"path/filepath"
 
 	"github.com/go-git/go-git/v5"
@@ -127,12 +129,22 @@ func main() {
 
 	defer out.Close()
 
+	switch ext := path.Ext(*outPath); ext {
+	case ".yaml":
 		out.Write([]byte("# dkl-dir2config " + Version + "\n"))
 
 		if err = yaml.NewEncoder(out).Encode(dst); err != nil {
 			log.Fatal("failed to render output: ", err)
 		}
 
+	case ".json":
+		if err = json.NewEncoder(out).Encode(dst); err != nil {
+			log.Fatal("failed to render output: ", err)
+		}
+
+	default:
+		log.Fatal("unknown output file extension: ", ext)
+	}
 }
 
 func cfgPath(subPath string) string { return filepath.Join(*dir, subPath) }