[FLINK-39797] Support disabling automatic table creation

[litiliu]

What is the purpose of the change

This pull request adds a Fluss pipeline sink option to disable automatic target table creation. When auto.create.table.enabled is set to false, the Fluss sink fails fast if the target table does not already exist, while preserving the existing default behavior of automatically creating tables.

JIRA: https://issues.apache.org/jira/browse/FLINK-39797

Brief change log

• Added optional Fluss sink option auto.create.table.enabled with default value true.
• Wired the option through FlussDataSinkFactory, FlussDataSink, and FlussMetaDataApplier.
• Updated create-table handling so missing target tables fail with ValidationException when automatic table creation is disabled.
• Kept database auto-creation and existing-table sanity checks unchanged.
• Added unit/integration coverage for accepting the new option and disabled auto-create behavior.

Verifying this change

This change is covered by existing and newly added tests.

Verified locally with:

mvn -pl flink-cdc-connect/flink-cdc-pipeline-connectors/flink-cdc-pipeline-connector-fluss -am -Dtest=FlussDataSinkFactoryTest,FlussMetadataApplierTest -DfailIfNoTests=false test

Result: Tests run: 19, Failures: 0, Errors: 0, Skipped: 0.

Documentation

Updated the English and Chinese Fluss pipeline connector documentation to describe auto.create.table.enabled and the pre-created table mode.