Delete old pipelines

What does this MR do and why?

Allow users to set pipeline expiry times per project and delete expired pipelines.

This won't work effectively with millions of projects, but that's expected. We want to see how popular this feature is before investing more time into building a robust solution.

References

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• #498969 (comment 2184896782)

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Screenshots or screen recordings

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How to set up and validate locally

1. In rails console enable the experiment fully

   Feature.enable(:ci_delete_old_pipelines)

2. Visit any project CI/CD settings pages such as http://127.0.0.1:3000/root/new-taggings/-/settings/ci_cd
3. Fill in Delete old pipelines with a desired value
4. Wait till the cron worker is executed(11 minutes tops).
5. Notice that 250 pipelines are gone.

Related to #498969