Add a Lookback Window on Cursor Based Postgres Connection

[tmas-definitive]

In the current design of the postgres source, a lookback window cannot be specified which would be extremely helpful in a cursor based replication strategy if a specific window of data needed to be replayed. I realize WAL or Xmin can probably handle this already, but if there are constraints to using cursor based (ie. pulling data from a read replica)

So now the query roughly generated on a cursor based run would be:

SELECT <columns> FROM <stream_source> WHERE cursor_field > {cursor_value}

Would like it to look something like

SELECT <columns> FROM <stream_source> WHERE cursor_field > {cursor_value} - {lookback}