Add "persistent_topic_size" to the list of "Notification Performance
Statistics" in doc/radosgw/notifications.rst.
Fixes: https://tracker.ceph.com/issues/71792
Signed-off-by: Zac Dover <zac.dover@proton.me>
Notification Performance Statistics
-----------------------------------
+- ``persistent_topic_size``: queue size in bytes.
- ``pubsub_event_triggered``: a running counter of events that have at least one topic associated with them
- ``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