Add hide_duplicate_runner_manager_fields_in_runner feature flag

🚨 🚨 NOTE: This MR should only be merged on Apr 29nd, in time for the 2nd breaking changes window (2024-04-29 09:00 UTC to 2024-05-01 22:00 UTC) 🚨 🚨

What does this MR do and why?

This MR adds a hide_duplicate_runner_manager_fields_in_runner so that we can safely remove the fields that have been copied from ci_runners to ci_runner_machines (see #415185).

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How to set up and validate locally

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I'm relying on the new tests and the existing (I've added pipeline:run-all-e2e pipeline:run-all-jest, and pipeline:run-all-rspec for added coverage).