Set crawl-stop in redis from operator when crawl is stopped (#815)

Change redis to <crawl-id>:crawl-stop to match webrecorder/browsertrix-crawler#303

backend/btrixcloud/operator.py

@@ -364,7 +364,7 @@ class BtrixOperator(K8sAPI):
             )
 
         if crawl.stopping:
-            await redis.set(f"{crawl.id}:stopping", "1")
+            await redis.set(f"{crawl.id}:crawl-stop", "1")
 
         # optimization: don't update db once crawl is already running
         # will set stats at when crawl is finished, otherwise can read