Verify background job to backfill user_details is finished

status blocked until %17.6

It will take some time for #462912 (closed) to finish. We need to verify it is finished before proceeding to the next step. Check the docs for the way to ensure background jobs are finished along with verifying their work.

• postgres ai row count verified as 0 meaning all work is done - https://console.postgres.ai/gitlab/gitlab-production-main/sessions/30776/commands/95585
  • updated row count shows 541 records https://console.postgres.ai/gitlab/gitlab-production-main/sessions/32857/commands/101269 - so we have some gap here, but we'll need to figure that out in a follow-up.
• no errors observed in Sentry
• This will need to be executed in %17.6 due to required stop coordination