[FLINK-23882][docs] Clarify TIMESTAMP WITH TIME ZONE is not supported by Flink SQL

[Vamsi-klu]

What is the purpose of the change

The data types reference page documents TIMESTAMP WITH TIME ZONE with full declaration syntax (TIMESTAMP(p) WITH TIME ZONE), which makes it look like a usable SQL type. In reality the type currently only exists as a logical type and is not supported by Flink SQL yet — reading/casting it is unimplemented (tracked by FLINK-20869), and the SQL JDBC driver explicitly throws:

TIMESTAMP WITH TIME ZONE is not supported, use TIMESTAMP or TIMESTAMP_LTZ instead

The missing caveat has repeatedly confused users (see FLINK-23882), who reach for TIMESTAMP WITH TIME ZONE expecting it to work and then hit timestamp-correctness surprises.

Brief change log

• Add a {{< hint warning >}} callout to the TIMESTAMP WITH TIME ZONE section of the data types reference stating the type only exists as a logical type, is not supported by Flink SQL yet (linking FLINK-20869), and pointing users to TIMESTAMP_LTZ when time zone information must be retained.
• Apply the same note to the Chinese (content.zh) mirror of the page.

Verifying this change

This change is a documentation-only update without test coverage. The claim was verified against the codebase: FlinkResultSet rejects TIMESTAMP_WITH_TIME_ZONE, and CastFunctionITCase leaves the casts unimplemented pending FLINK-20869. The note reuses the {{< hint warning >}} shortcode already present elsewhere on the same page.

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? docs (this PR is the doc change)

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This documentation change was prepared with AI assistance (Claude Code).

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CI report:

• de5f8c4 Azure: SUCCESS

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[Vamsi-klu]

This is a docs-only change (en + zh) clarifying that TIMESTAMP WITH TIME ZONE is not supported in Flink SQL and pointing users to TIMESTAMP_LTZ. The behavior is verified against the JDBC driver, which throws ... not supported, use TIMESTAMP or TIMESTAMP_LTZ, and the related cast tests remain gated on FLINK-20869. Would a committer be able to take a look when convenient? Happy to adjust the wording.

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Drafted-by: Claude Code (Opus 4.8) (no human review before posting)