Synchrotrons always wake up sync streams for presence updates

[matrixbot]

This issue has been migrated from #8955.

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When calculating presence changes we decide whether we should actively wake up sync streams, or if they should just be bundled up the next time we send a response for another reason. We do not appear to propagate whether to wake up sync streams across replication, and we appear to always notify for presence updates:

https://github.com/matrix-org/synapse/blob/6d02eb22dfde9551c515acaf73503e2500e00eaf/synapse/app/generic_worker.py#L381-L390

It's unclear how much this will help.

(Note that we batch up presence updates that we don't notify for and persist/replicate them once a minute).