Backend: Create an endpoint for export file data in CSV format; transform Dynamo data for timesheet into CSV formatted data and return

[izzyconner]

[izzyconner]

For reference: https://medium.com/@darshana_18428/downloading-csv-using-post-request-in-node-js-and-angular-a581f97ed493

[izzyconner]

Initial stubbing between frontend and backend complete and working with mock data; downloads the CSV correctly