add option to change filter_mode

roles/matrix-bridge-mautrix-telegram/templates/config.yaml.j2

@@ -273,7 +273,7 @@ bridge:
         # Filter mode to use. Either "blacklist" or "whitelist".
         # If the mode is "blacklist", the listed chats will never be bridged.
         # If the mode is "whitelist", only the listed chats can be bridged.
-        mode: blacklist
+        mode: "{{ matrix_mautrix_telegram_filter_mode }}"
         # The list of group/channel IDs to filter.
         list: []