migrate 392 questions to pattern format

backend/data/questions/can-convert-string-in-k-moves.yaml

@@ -7,7 +7,8 @@ categories:
   - strings
   - hash-tables
 patterns:
-  - greedy
+  - slug: greedy
+    is_optimal: true
 
 function_signature: "def can_convert_string(s: str, t: str, k: int) -> bool:"