fix: `BATCH` sync does not record a max replication key value in emitted `STATE`

[aaronsteers]

Related to:

• meltano/sdk#976

As noted there, the simply fix is to run a SELECT max(<replication_key>) FROM <table> prior to querying the batches. The developer can then leverage this in get_batches() for subsequent sync using the normal get_replication_key_value() method, and then filtering the query to be limited by the max replication key value.