[hotfix][doc] add javadoc for describing ITCASE_USE_MINICLUSTER rule in details

[JingGe]

What is the purpose of the change

When the developer runs into some violation checks of the ITCase rules, they may need some more information about the rule definition. Sometimes, the rule itself goes complex. It will be helpful to add details explanation for such rule so the developer knows how to fix the violations.

Brief change log

• add javadoc with comprehensive introduction of the rule ITCASE_USE_MINICLUSTER

Verifying this change

This change is a trivial javadoc improvement without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)

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CI report:

• 1a7ff3e Azure: SUCCESS

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Automated Checks

Last check on commit d98b4c8 (Wed Feb 09 23:16:50 UTC 2022)

Warnings:

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Review Progress

• ❓ 1. The [description] looks good.
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• ❓ 5. Overall code [quality] is good.

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