Add Requeue backfill post migration for User Addon Assignments

What does this MR do and why?

The problem is ongoing because:

1. GitlabSubscriptions::Duo::BulkAssignService uses upsert_all which bypasses ActiveRecord callbacks
2. Other services may also bypass callbacks when creating addon assignments
3. This leads to missing historical data in ClickHouse for addon assignments

This migration will identify AddPn assignments without corresponding Papertrail versions and create the missing records with proper event='create' and correct timestamps. We have run this migration before so that has been already tested in !196272 (merged)

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How to set up and validate locally

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Related to #566534 (closed)