Merge branch ApplicationClusterManager

[xyuanlu]

Issues

• My PR addresses the following Helix issues and references them in the PR description:

#2589
#2594

Description

• Here are some details about my PR, including screenshots of any UI changes:

Merge branch ApplicationClusterManager. Including following changes:
[Add supporting APIs a isEvacuateFinished and isReadyForPreparingJoini…]
[Change instance operation orthogonal to instance enable (]
[Add on-demand rebalance API (]
[Fix NPR error in test for TestDelayedAutoRebalanceWithRackaware (]
[Add support for node evacuation. (]
[Add CI test config for ApplicationClusterManager branch (]
[Instance Evacuation operation sanity check ]
[Implement the on-demand rebalance service (]
[Add API for Instance evacuation (]

Tests

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Please refer to original PRs

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Changes that Break Backward Compatibility (Optional)

• My PR contains changes that break backward compatibility or previous assumptions for certain methods or API. They include:

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Documentation (Optional)

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Commits

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  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Code Quality

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