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One approach is for the controller to allow unregistering controllers non-durably if the metadata version does not support the UnregisterControllerRecord. This gives operators a path to migrate existing clusters onto a MV that supports this record, where they can persist the unregister record. One issue with this approach is that the UX is not good, requiring the user to unregister the controller twice.

Test Plan

Add an integration test for unregistering a controller in both static quorum and dynamic quorum clusters. 

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