Maintenance mode stacking support

[LZD-PratyushBhatt]

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This PR closes #3041 , adds support for Maintenance mode Stacking.

Description

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The current implementation of maintenance mode for clusters supports only a single reason at a time, tracked using the simpleFields.REASON key. This restricts the functionality to a single actor and reason, which limits flexibility and coordination.

This proposal introduces a new design that allows multiple actors to independently place a cluster into maintenance mode for different reasons. We will extend the maintenance mode design to support multiple actors, each capable of independently adding or removing their own maintenance reason. The cluster will remain in maintenance mode as long as at least one active reason exists. Each reason will be associated with metadata such as the actor, reason, and timestamp. For backwards compatibility, the existing simpleFields.REASON will be retained and updated to reflect the most recent active reason. If a reason is removed, it will be replaced with the next most recent one. While legacy clients that remove the entire znode cannot be completely prevented, we will handle such cases gracefully and recommend migrating to an updated API that enables proper multi-actor maintenance handling.

Tests

• The following tests are written for this issue:
  testAutomationMaintenanceMode, testRemoveMaintenanceReasonNoDuplicates, testLegacyClientCompatibility, testMaintenanceHistoryAfterOperationFlag, testMultiActorMaintenanceModeExitSequence, testMultiActorMaintenanceModeReconciliation, testMultiActorMaintenanceModeOldClientExit, testMultiActorMaintenanceModeOldClientOverride, testMultiActorMaintenanceModeInvalidExit

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[LZD-PratyushBhatt]

Hi @junkaixue , @GrantPSpencer , @zpinto , @xyuanlu
Can you please review this PR? Its for supporting MM stacking.

[xyuanlu]

This can be dangerous. What if the new version read an old ZNode.

[junkaixue]

Highly recommend the new contributor starting with stablizing the tests instead of touch the very core part. It is very very dangerous. There was one line log change can blast the entire server before.

If you still believe your change is solid, we can help review. At the same time, please never lower the bar.