Improve appservice handler to send only the most recent read receipts when no stream_id is stored. (#8744)

* Make this line debug (it's noisy)

* Don't include from_key for presence if we are at 0

* Limit read receipts for all rooms to 100

* changelog.d/8744.bugfix

* Allow from_key to be None

* Update 8744.bugfix

* The from_key is superflous

* Update comment

synapse/handlers/appservice.py

@@ -226,7 +226,7 @@ class ApplicationServicesHandler:
         new_token: Optional[int],
         users: Collection[Union[str, UserID]],
     ):
-        logger.info("Checking interested services for %s" % (stream_key))
+        logger.debug("Checking interested services for %s" % (stream_key))
         with Measure(self.clock, "notify_interested_services_ephemeral"):
             for service in services:
                 # Only handle typing if we have the latest token