add default for TG filter_mode

roles/matrix-bridge-mautrix-telegram/defaults/main.yml

@@ -38,6 +38,9 @@ matrix_mautrix_telegram_api_id: ''
 matrix_mautrix_telegram_api_hash: ''
 matrix_mautrix_telegram_bot_token: disabled
 
+# Define the filter-mode
+matrix_mautrix_telegram_filter_mode: "blacklist"
+
 # Whether or not the public-facing endpoints should be enabled (web-based login)
 matrix_mautrix_telegram_appservice_public_enabled: true