(Applies to the Grafana graphs)
As discovered by @devonh, we use `synapse_storage_events_persisted_events_total` (which tracks *all* persisted events) for the "Events" rate in the "Event Send Time Quantiles" graph. This is pretty misleading as I would expect it to be the rate of events being sent given the graph title, "Event Send Time Quantiles".
Since the event persistence queues are shared for local and remote events from federation and will block local events being sent, I think it does still make sense to have the event persist rate. I've updated the graph to include the rate of "Local events being persisted" and the rate of "All events being persisted". I think this properly disambiguates and clarifies what the graph is trying to show.
e80bc4b062