Backfill archived for work_items

What does this MR do and why?

This is a follow-up to !124846 (merged). It turned out that we now index WorkItem since it's a subclass of Issue.

In this MR we're going to backfill archived for these documents.

Migration runtime

> batch_size = 9_000
=> 9000
> throttle_delay = 1.minute
=> 1 minute
> number_of_documents = 167_616
=> 167616
> (number_of_documents / batch_size) * throttle_delay
=> 18 minutes

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #418792 (closed)