[FLINK-40497][table] Allow materialized tables to default to ON CONFLICT DO ERROR

[gustavodemorais]

What is the purpose of the change

A materialized table has no syntax for an explicit ON CONFLICT clause, so it always falls back to the implicit DO DEDUPLICATE strategy when its primary key differs from its query's upsert key. This adds an opt-in option to default it to DO ERROR instead, avoiding the state-heavier deduplicating materializer, applied only when every source already declares a watermark so table creation never fails because of it.

Brief change log

• Add TABLE_EXEC_SINK_MATERIALIZED_TABLE_FORCES_ON_CONFLICT_ERROR, default false.
• convertMaterializedTableAsToRel picks ON CONFLICT DO ERROR when the option is enabled and every source has a watermark, otherwise keeps the previous behavior.
• Add allSourcesHaveWatermarks, walking the logical input tree to check each source's watermark spec.
• Thread getTableConfig through PlannerBase's call to convertMaterializedTableAsToRel.
• Tailor the require-on-conflict validation message with a materialized-table-specific hint when the new option is enabled but a source is missing a watermark.
• Document the new option and its interaction with require-on-conflict in the INSERT reference docs.

Verifying this change

• ExplainTest

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): yes - new option added to ExecutionConfigOptions (@PublicEvolving)
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? (docs/content/docs/sql/reference/dml/insert.md, docs/content.zh/docs/sql/reference/dml/insert.md, generated config option docs)

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2.1.235 (Claude Code) with Sonnet 5

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CI report:

• 49a67f3 Azure: FAILURE

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[raminqaf]

Left a comment

[raminqaf]

We can simplify this

private static boolean allSourcesHaveWatermarks(RelNode rel) {
    if (rel instanceof TableScan) {
        final TableSourceTable table =
                ((TableScan) rel).getTable().unwrap(TableSourceTable.class);
        return table == null
                || !table.contextResolvedTable().getResolvedSchema().getWatermarkSpecs().isEmpty();
    }
    return rel.getInputs().stream().allMatch(DynamicSinkUtils::allSourcesHaveWatermarks);
}

[raminqaf]

Also noticed that collectSourcesWithoutWatermarks does the same check