Initialize the conversion for shared_runners_duration

What does this MR do and why?

Initialize the conversion for shared_runners_duration from integer to bigint.

Because the change_column_type_concurrently isn't working, we need to follow this guideline to convert shared_runners_duration to bigint:

https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html#initialize-the-conversion-and-start-migrating-existing-data-release-n

And this MR is the first step to convert shared_runners_duration to bigint

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 #420394 (closed)