Uniqueness of Batch IDs

[hgrano]

The settlement Batch IDs can be re-used in different settlements. Due to the way contract keys work, the same contract key can be used again as long as the old contract was archived. Hence we can have multiple Batches in the PQS database with the same requestors and ID. Therefore when we run queries for the /settlements endpoint, this could cause issues, as the queries assume uniqueness of the Batch IDs. Perhaps there is a better way to join Batches with Instructions to avoid this issue.