whatsapp bridge: set the default log level to warning

Debug logs are inappropriate for production use.

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

@@ -131,4 +131,4 @@ matrix_mautrix_whatsapp_bridge_encryption_key_sharing_allow: "{{ matrix_mautrix_
 
 # Minimum severity of journal log messages.
 # Options: debug, info, warn, error, fatal
-matrix_mautrix_whatsapp_log_level: 'debug'
+matrix_mautrix_whatsapp_log_level: 'warn'