migrate 392 questions to pattern format

backend/data/questions/coin-change.yaml

@@ -7,7 +7,8 @@ categories:
   - dynamic-programming
   - arrays
 patterns:
-  - dynamic-programming
+  - slug: dynamic-programming
+    is_optimal: true
 
 function_signature: "def coin_change(coins: list[int], amount: int) -> int:"