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

The data types reference presents TIMESTAMP WITH TIME ZONE with full
declaration syntax but never states that the type only exists as a
logical type and is not usable in Flink SQL yet (tracked by FLINK-20869;
the SQL JDBC driver even throws "TIMESTAMP WITH TIME ZONE is not
supported, use TIMESTAMP or TIMESTAMP_LTZ instead"). This has repeatedly
confused users on the mailing list.

Add a warning callout to the English and Chinese data-types reference
pages stating the type is unsupported and pointing users to TIMESTAMP_LTZ.

Author: Vamsi-klu

docs/content.zh/docs/sql/reference/data-types.md

@@ -812,6 +812,12 @@ Data type of a timestamp *with* time zone consisting of `year-month-day hour:min
 with up to nanosecond precision and values ranging from `0000-01-01 00:00:00.000000000 +14:59` to
 `9999-12-31 23:59:59.999999999 -14:59`.
 
+{{< hint warning >}}
+`TIMESTAMP WITH TIME ZONE` currently only exists as a logical type and is **not supported** by Flink SQL yet
+(tracked by [FLINK-20869](https://issues.apache.org/jira/browse/FLINK-20869)). If you need to retain time zone
+information, use `TIMESTAMP_LTZ` instead.
+{{< /hint >}}
+
 {{< tabs "timestamps" >}}
 {{< tab "SQL/Java/Scala" >}}
 Compared to the SQL standard, leap seconds (`23:59:60` and `23:59:61`) are not supported as the semantics

docs/content/docs/sql/reference/data-types.md

@@ -820,6 +820,12 @@ Data type of a timestamp *with* time zone consisting of `year-month-day hour:min
 with up to nanosecond precision and values ranging from `0000-01-01 00:00:00.000000000 +14:59` to
 `9999-12-31 23:59:59.999999999 -14:59`.
 
+{{< hint warning >}}
+`TIMESTAMP WITH TIME ZONE` currently only exists as a logical type and is **not supported** by Flink SQL yet
+(tracked by [FLINK-20869](https://issues.apache.org/jira/browse/FLINK-20869)). If you need to retain time zone
+information, use `TIMESTAMP_LTZ` instead.
+{{< /hint >}}
+
 {{< tabs "timestamps" >}}
 {{< tab "SQL/Java/Scala" >}}
 Compared to the SQL standard, leap seconds (`23:59:60` and `23:59:61`) are not supported as the semantics