Allow any worker type in cookiecutter

cookiecutter.json

@@ -2,14 +2,7 @@
   "slug": "demo",
   "name": "Demo",
   "description": "Demo ML worker for Arkindex",
-  "worker_type": [
-    "classifier",
-    "recognizer",
-    "ner",
-    "dla",
-    "word-segmenter",
-    "paragraph-creator"
-  ],
+  "worker_type": "demo",
   "author": "",
   "email": ""
 }