Explore BLOB support via re-selection

This came up in a conversation with rhn-support-bibryam: could we have a story for CLOB/BLOB by means of an SMT (could be baked into the connector later on) which selects the value from the DB when encountering some specific placeholder value?

Of course this would be subject to the same semantics as the MongoDB connector with full image: in case of multiple changes in close timely proximity, always the latest value would be emitted, not necessarily the value as it was at the time of producing a specific event.

I still think it's worth exploring as a cheap option for CLOB/BLOB support.