Pull upstream mautrix-slack config defaults

roles/custom/matrix-bridge-mautrix-slack/templates/config.yaml.j2

@@ -28,10 +28,11 @@ appservice:
 
     # Database config.
     database:
-        # The database type. "sqlite3" and "postgres" are supported.
+        # The database type. "sqlite3-fk-wal" and "postgres" are supported.
         type: {{ matrix_mautrix_slack_appservice_database_type|to_json }}
         # The database URI.
-        #   SQLite: File name is enough. https://github.com/mattn/go-sqlite3#connection-string
+        #   SQLite: A raw file path is supported, but `file:<path>?_txlock=immediate` is recommended.
+        #           https://github.com/mattn/go-sqlite3#connection-string
         #   Postgres: Connection string. For example, postgres://user:password@host/database?sslmode=disable
         #             To connect via Unix socket, use something like postgres:///dbname?host=/var/run/postgresql
         uri: {{ matrix_mautrix_slack_appservice_database_uri|to_json }}
@@ -57,6 +58,11 @@ appservice:
     # Requires MSC2409 support (i.e. Synapse 1.22+).
     ephemeral_events: true
 
+    # Should incoming events be handled asynchronously?
+    # This may be necessary for large public instances with lots of messages going through.
+    # However, messages will not be guaranteed to be bridged in the same order they were sent in.
+    async_transactions: false
+
     # Authentication tokens for AS <-> HS communication. Autogenerated; do not modify.
     as_token: {{ matrix_mautrix_slack_appservice_token | to_json }}
     hs_token: {{ matrix_mautrix_slack_homeserver_token | to_json }}