migrate 392 questions to pattern format

backend/data/questions/find-median-from-data-stream.yaml

@@ -7,7 +7,8 @@ categories:
   - heap
   - sorting
 patterns:
-  - heap
+  - slug: heap
+    is_optimal: true
 
 function_signature: "class MedianFinder:\n    def __init__(self): ...\n    def add_num(self, num: int) -> None: ...\n    def find_median(self) -> float: ..."