doc/radosgw: improve "pubsub_push_pending" info

Explain in greater detail what the counter "pubsub_push_pending" counts.

Fixes: https://tracker.ceph.com/issues/71793

Signed-off-by: Zac Dover <[email protected]>
(cherry picked from commit 26f2c0e)

Author: zdover23

doc/radosgw/notifications.rst

@@ -129,7 +129,10 @@ Notification Performance Statistics
 - ``pubsub_event_lost``: a running counter of events that had topics associated with them, but that were not pushed to any of the endpoints
 - ``pubsub_push_ok``: a running counter, for all notifications, of events successfully pushed to their endpoints
 - ``pubsub_push_fail``: a running counter, for all notifications, of events that failed to be pushed to their endpoints
-- ``pubsub_push_pending``: the gauge value of events pushed to an endpoint but not acked or nacked yet
+- ``pubsub_push_pending``: the gauge value of events pushed to an endpoint but
+  not acked or nacked yet. This does not include the notifications waiting in
+  the persistent queue. Only the notifications that are in flight in both
+  persistent and non-persistent cases are counted.
 
 .. note::