Change Assessments query to differential

[KyleEvers]

🐛 Bug Report

The assessments findings is sending the entire database over, but it should be a differential. Because the quality of the data being sent has been in flux we have opted to send the entire database daily. This should be changed to a differential to only send over new/changed records in the daily feed.

See lines here
https://github.com/cisagov/cyhy-feeds/blob/develop/aws_jobs/cyhy-data-extract.py#L283-L286

The query should add

                '$gte': start_of_data_collection,
                '$lt': end_of_data_collection

Where the data being checked it the last modified date for the document.