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1. UnregisterControllerRequest is sent to the active controller
2. The active controller writes an UnregisterControllerRecord to the metadata log
3. When this record is committed, return a response to the user for unregistering the controller
4. The active controller's state machine removes the registration for controller 9990, meaning feature upgrades no longer consider node 9990's supported features
5. The registration from controller 9990 is removed from the metadata image, so it will not be in future snapshots

kafka-metadata-quorum 

Add the --unregister flag to the kafka-metadata-quorum remove-controller command. When this flag is set, invoking this command will remove the controller as a KRaft voter and unregister it. Below is an example invocation.

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1. RemoveRaftVoterRequest  is sent to the active controller
2. The KRaft leader writes a VotersRecord without voter 9990 to the metadata log
3. When this record is committed, return a response to the user for removing the voter
4. UnregisterControllerRequest is sent to the active controller
5. The active controller writes an UnregisterControllerRecord to the metadata log
6. When this record is committed, return a response to the user for unregistering the controller
7. The active controller's state machine removes the registration for controller 9990, meaning feature upgrades no longer consider node 9990's supported features
8. The registration from controller 9990 is removed from the metadata image, so it will not be in future snapshots

Proposed Changes

Controller Changes

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