Add option to logical topic router for controlling placement of table information

Currently, the table info is always added to the message key, allowing to keep apart records with the same id from multiple shards. There are use cases for the router though where this isn't desirable, e.g. partitioned tables in Postgres. Here change events originate from different partition tables, but keys are already unique. So it should be possible to leave keys unchanged, optionally adding the source table name as a header attribute.