Create year-end forms report

When a Year-End Forms Report is created, the report content will be created asynchronously. It may then be retrieved from the GET endpoint using an "accept: text/csv" header.

This report has one sheet per form type: t4, t4a and rl1. A CSV holds a single sheet, and no sheet is a stand-in for the others, so a CSV request must name one with ?sheet= or it returns 422. Requesting the Excel format instead returns all three sheets in one file.

To filter which payrolls should be included in the report, you must pass a filters object here, which must contain: year: The year to generate the report for.