adding new attribute lock (#8)

_tests/configurations/wrong-command-template-gotenberg.yml

@@ -3,6 +3,7 @@ logs:
   level: "DEBUG"
   formatter: "text"
 commands:
+  lock: true
   merge:
     template: "pdftk {{ range $filePath := .FilesPaths }} {{ $filePath }} {{ end }} cat output {{ .ResultFilePath }}"
     interpreter: "/bin/sh -c"