[FLINK-38262][table] show connections operation

[Shekharrajak]

What is the purpose of the change

Adds ShowConnectionsOperation and converter support for SHOW CONNECTIONS, including catalog/database qualification and LIKE filtering.

Ref https://issues.apache.org/jira/browse/FLINK-38262

Brief change log

Add SHOW CONNECTION operation

Verifying this change

Unit tests and IT

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

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

Documentation

• Does this pull request introduce a new feature? (yes / no) yes
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Was generative AI tooling used to co-author this PR?

• Yes

[flinkbot]

CI report:

• f0455b5 UNKNOWN
• df55cc1 Azure: SUCCESS

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[snuyanzin]

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