Add topics to problem 'binary-search' #938 (#999)

Add topics to problem 'binary-search' #938

config.json

       "core": true,
       "difficulty": 6,
       "slug": "binary-search",
-      "topics": null,
+      "topics": [
+        "recursion",
+        "arrays",
+        "searching",
+        "generics"
+      ],
       "unlocked_by": null,
       "uuid": "50136dc3-caf7-4fa1-b7bd-0cba1bea9176"
     },
   ],
   "language": "Java",
   "solution_pattern": "reference"
-}
+}