Add override FF for deleting old pipelines

What does this MR do and why?

Some projects create pipelines only on the default branch which is protected by default and we need a way to override the setting to delete those pipelines.

References

• https://gitlab.com/gitlab-org/gitlab/-/issues/515449#note_2742766344
• https://docs.gitlab.com/development/feature_flags/controls/#selectively-disable-by-actor

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