:auto-ts grouping by specific timestamp type

It would be great to be able to auto-group based on specifically `CLOSED`, `SCHEDULED` or `DEADLINE` timestamp only, rather than the latest timestamp of any type, e.g. specify `(:auto-ts CLOSED)` or `(:auto-closed t)` or something like that.

As an example, I have an org-ql view that shows tasks completed in the last 2 weeks and uses `:auto-ts` to group them by what day they were closed. Mostly that works, because mostly the `CLOSED` date is the latest timestamp, but where there's a deadline and I completed the task before the deadline, the deadline is used instead because that timestamp is later.