fix: Outbox must skip dbz_signal

[miguelbirdie]

Outbox is a Kafka Connect transformer to redirect the integration event to the right topic. The logic assumes that there is a field called payload, and that's true for integration events.
However, if we want to enable incremental snapshots, automatically the connector starts ingesting public.dbz_signal table used to managed custom snapshots. But that table doesn't contain payload field. So, we are going to skip in Outbox transformer all messages coming from public.dbz_signal topic.