Prepare route for daqbook service records

[rhythmatician]

In order to reduce the number of steps to prepare a workbook for offline use, lets create an API route that provides this:

SELECT DISTINCT ON (asset_id) asset_id, certificate_tn, service_date, due_date
FROM daqbook_service_records
ORDER BY asset_id, service_date DESC;

In order to do this, we'll need to add the due_date column to the table, and make sure it populates, as well.