Change logging of puppeted requests to better differentiate users (#10779)

This used to be a comma and got accidentally changed to a period in #9654, but a pipe character is more easier to parse visually.

changelog.d/10779.misc

@@ -0,0 +1 @@
+Change the format of authenticated users in logs when a user is being puppeted by and admin user.

synapse/http/site.py

@@ -384,7 +384,7 @@ class SynapseRequest(Request):
         # authenticated (e.g. and admin is puppetting a user) then we log both.
         requester, authenticated_entity = self.get_authenticated_entity()
         if authenticated_entity:
-            requester = f"{authenticated_entity}.{requester}"
+            requester = f"{authenticated_entity}|{requester}"
 
         self.site.access_logger.log(
             log_level,