Refactor stoppable check logic for enhanced zone analysis

[MarkGaox]

Issues

• My PR addresses the following Helix issues and references them in the PR description:
• Cross-zone Stoppable Check #2655

(#200 - Link your issue number here: You can write "Fixes #XXX". Please use the proper keyword so that the issue gets closed automatically. See https://docs.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue
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Description

• Here are some details about my PR, including screenshots of any UI changes:
• Add support to randomly select zone order for the single-zone stoppable check.
• Modify the logic for stoppable instance checks within a single zone to target the zone with the highest instance count if the order of zone is not specified.

(Write a concise description including what, why, how)

Tests

• The following tests are written for this issue:
• mvn test -Dtest=TestInstancesAccessor

[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 51.578 s - in org.apache.helix.rest.server.TestInstancesAccessor
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] 
[INFO] --- jacoco:0.8.6:report (generate-code-coverage-report) @ helix-rest ---
[INFO] Loading execution data file /Users/xiaxgao/IdeaProjects/helix_ps/helix-rest/target/jacoco.exec
[INFO] Analyzed bundle 'Apache Helix :: Restful Interface' with 94 classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  55.978 s
[INFO] Finished at: 2023-10-10T17:40:54-07:00
[INFO] ------------------------------------------------------------------------

(List the names of added unit/integration tests)

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

(If CI test fails due to known issue, please specify the issue and test PR locally. Then copy & paste the result of "mvn test" to here.)

Changes that Break Backward Compatibility (Optional)

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

(Consider including all behavior changes for public methods or API. Also include these changes in merge description so that other developers are aware of these changes. This allows them to make relevant code changes in feature branches accounting for the new method/API behavior.)

Documentation (Optional)

• In case of new functionality, my PR adds documentation in the following wiki page:

(Link the GitHub wiki you added)

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
  (helix-style-intellij.xml if IntelliJ IDE is used)

[MarkGaox]

This PR is approved by @xyuanlu . Thanks!
Final commit message:
Refactor the zone-based stoppable check logic and add support to randomly select zone order for the zone-based stoppable check.