Adding the sensors in DistClusterControllerStateModel

[vivek8420]

Issues

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

• We encountered an issue where an instance assumed leadership of the cluster. However, after a leadership change, the cleanup process completed, but the leader information was not properly removed. As a result, no other instance was able to acquire leadership.
• This failure was silent — there were no notifications or alerts generated.
• To address this, we are adding sensors to detect this scenario, enabling us to build visualizations and improve observability.

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Description

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Tests

• The following tests are written for this issue:

(List the names of added unit/integration tests)

• testLeadershipFailureMetrics: Tests that ClusterStatusMonitor correctly tracks and reports leadership failure events through JMX metrics.
• testStillLeaderDuringResetMetrics: Tests that ClusterStatusMonitor correctly tracks controllers that remain leader during reset operations.
• testOnBecomeLeaderFromStandby_whenMultipleInstancesTrigger: Tests that when multiple controllers compete for leadership, only one succeeds and leadership failures are properly tracked.

• The following is the result of the "mvn test" command on the appropriate module:

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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

• My commits all reference appropriate Apache Helix GitHub issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  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

• My diff has been formatted using helix-style.xml
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[proud-parselmouth]

LGTM. Just made a minor comment