Starts a background job to generate an 'annotator' or 'item' report.
Immediately returns job info, containing the file URL to get the report from.

Note:

• The 'annotator' report data is available from 2024-11-05
• The 'item' report data is available from 2025-08-01
• All times are UTC. Every row of the report file has period_start and period_end (ISO 8601, end exclusive): the range the report covers, which is start raised to the date above for its type and stop capped at the time the job ran. They are the last two CSV columns. timestamp is a deprecated alias of period_start.