Added topics for sublist problem (#928)

* Added topics for sublist problem

* Added enumeration and generics to sublist topics

* Added topics for sublist problem

config.json

       "core": false,
       "difficulty": 7,
       "slug": "sublist",
-      "topics": null,
+      "topics": [
+        "lists",
+        "searching",
+        "loops",
+        "generics",
+        "enumeration"
+      ],
       "unlocked_by": "linked-list",
       "uuid": "d2aedbd7-092a-43d0-8a5e-ae3ebd5b9c7f"
     },