[FLINK-38262][table] describe connection operation

[Shekharrajak]

What is the purpose of the change

Adds DescribeConnectionOperation and converter support for DESCRIBE CONNECTION, with masked sensitive values and extended metadata.

Brief change log

Add DESCRIBE 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:

• 805f418 Azure: SUCCESS

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[snuyanzin]

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