queue: Increase paging thresholds for deferred_work queue.

This queue is used to things which definitionally may take longer than
a request, so paging after 60s is rather aggressive.  This is
especially true because this queue has a very long tail of very slow
tasks -- p99 of task time in this queue is 8.5s, while p99.9 is 197s.

Raise the paging threshold to 15 minutes.  While there are
semi-user-facing tasks which use this queue (primarily marking
messages as read), those being delayed for minutes is already a real
possibility if they are stuck behind a large realm export -- and this
is not a situation which should necessarily page, since it is not
solvable by the administrator.

scripts/lib/check_rabbitmq_queue.py

@@ -38,12 +38,14 @@ states = {
 
 MAX_SECONDS_TO_CLEAR: DefaultDict[str, int] = defaultdict(
     lambda: 30,
+    deferred_work=600,
     digest_emails=1200,
     missedmessage_mobile_notifications=120,
     embed_links=60,
 )
 CRITICAL_SECONDS_TO_CLEAR: DefaultDict[str, int] = defaultdict(
     lambda: 60,
+    deferred_work=900,
     missedmessage_mobile_notifications=180,
     digest_emails=1800,
     embed_links=90,