Implemented writing JSON as string and converting struct to json

[chernser]

Summary

• Adds JSON as a valid type
• Updates schema validation to react on input_format_binary_read_json_as_string
• Updates write to encode JSON as string in case of binary format or write as a string if it is already one

Closes: #543

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[chernser]

/windsurf review

[Copilot]

Pull Request Overview

This PR introduces support for a new JSON type in ClickHouse sink connector, updating type dispatch, writer logic, and adding tests to cover JSON serialization in both schema-based and schemaless modes.

• Adds JSON to Type enum and dispatch logic in Column
• Extends ClickHouseWriter to conditionally write JSON as string under binary format
• Adds helper methods and tests for JSON record generation and end-to-end validation

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/test/java/.../SchemalessTestData.java	New createJSONType to generate schemaless JSON SinkRecords
src/test/java/.../SchemaTestData.java	New createJSONType to generate schema-based JSON SinkRecords
src/test/java/.../ClickHouseTestHelpers.java	Bumped default ClickHouse version for tests
src/test/java/.../ClickHouseSinkTaskWithSchemaTest.java	Added test for writing JSON with RowBinary+input_format_binary_read_json_as_string
src/test/java/.../ClickHouseSinkTaskSchemalessTest.java	Added schemaless JSON writing test
src/main/java/.../db/mapping/Type.java	Added JSON enum
src/main/java/.../db/mapping/Column.java	Dispatches JSON type for JSON columns
src/main/java/.../db/ClickHouseWriter.java	Implements JSON writing logic using GSON and new config flag

Comments suppressed due to low confidence (2)

src/main/java/com/clickhouse/kafka/connect/sink/db/ClickHouseWriter.java:77

• The variable name binaryFormatWrtiteJsonAsString contains a typo; consider renaming it to binaryFormatWriteJsonAsString for clarity.

    private boolean binaryFormatWrtiteJsonAsString = false;

src/main/java/com/clickhouse/kafka/connect/sink/db/ClickHouseWriter.java:556

• Consider adding a unit or integration test to cover this error path when input_format_binary_read_json_as_string is not set, ensuring this exception is thrown as expected.

                    throw new RuntimeException("Writing JSON in binary is not supported yet. Use `input_format_binary_read_json_as_string=1` in clickhouse settings to allow writing as string");