Add logging on startup/shutdown (#8448)

This is so we can tell what is going on when things are taking a while to start up.

The main change here is to ensure that transactions that are created during startup get correctly logged like normal transactions.

scripts/synapse_port_db

@@ -489,7 +489,7 @@ class Porter(object):
 
         hs = MockHomeserver(self.hs_config)
 
-        with make_conn(db_config, engine) as db_conn:
+        with make_conn(db_config, engine, "portdb") as db_conn:
             engine.check_database(
                 db_conn, allow_outdated_version=allow_outdated_version
             )