Swapping columns for ci_pipelines for self-host

What does this MR do and why?

This is to introduce the migration to swap bigint conversion columns for self-host:

• ci_pipelines.auto_canceled_by_id
• ci_pipelines.auto_canceled_by_id_convert_to_bigint

See:

• https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html#swap-the-columns-release-n--1
• !134597 (merged): MR to finalize column swap on prod
• #422810 (comment 1621453615): migration succeeded on prod

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Before	After

How to set up and validate locally

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MR acceptance checklist

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Related to #422810 (closed)