[FLINK-21849][sql-client] Add default module test case for 'SHOW [FULL] MODULES'

[LadyForest]

What is the purpose of the change

*This pull request adds a case in CliClientITCase to test SHOW [FULL] MODULES for the default core module.

Brief change log

• Add SHOW MODULES and SHOW FULL MODULES in module.q

Verifying this change

This change is can be verified by running CliClientITCase.

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/Mesos, 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)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[fsk119]

Thanks for your contribution. LGTM

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Automated Checks

Last check on commit bdecb09 (Thu Mar 18 08:58:01 UTC 2021)

Warnings:

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CI report:

• bdecb09 Azure: SUCCESS

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[wuchong]

LGTM.