ticdc: document ignore-update-only-columns filter

[lidezhu]

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Summary by CodeRabbit

• 文档
  • 新增 ignore-update-only-columns 配置说明，用于过滤仅更新指定列的 UPDATE 事件。
  • 明确该配置仅对 Kafka 下游生效；涉及主键或唯一键变更的事件不会被过滤。
  • 补充配置版本、大小写匹配、无效列处理及非 Kafka 下游行为说明。
  • 在 OpenAPI v2 的创建、查询和更新示例中新增对应配置字段。

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📒 Files selected for processing (3)

• ticdc/ticdc-changefeed-config.md
• ticdc/ticdc-filter.md
• ticdc/ticdc-open-api-v2.md

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📝 Walkthrough

Walkthrough

文档新增 ignore-update-only-columns 配置，说明其 Kafka 下游行为、过滤规则和例外条件，并在 OpenAPI v2 的创建、查询及更新示例中加入对应字段。

Changes

UPDATE 列过滤配置

Layer / File(s)	Summary
事件过滤配置说明 ticdc/ticdc-changefeed-config.md, ticdc/ticdc-filter.md	新增 ignore-update-only-columns 配置及示例。文档说明 Kafka 下游限制、列变更过滤规则、主键或唯一键变更例外、大小写匹配、无效列处理和非 Kafka 下游行为。
OpenAPI v2 字段同步 ticdc/ticdc-open-api-v2.md	在同步任务创建、查询响应和更新请求示例中加入 ignore_update_only_columns，并补充参数说明。

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🔵 Low · up to f4a53

The documentation for ignore_update_only_columns does not describe the primary-key and unique-key exception or clarify that INSERT and DELETE events are unaffected. This is a bounded documentation risk and the PR is mergeable with explicit owner follow-up to correct the description.

Suggested labels: requires-version-specific-changes

Suggested reviewers: 3aceshowhand

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	PR 描述未填写“变更内容”必填部分，缺少本次文档变更的具体说明和原因。	补充变更内容及原因，并确认 master 和 v8.5 版本选择与实际变更范围一致。

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	标题准确概括了为 TiCDC 文档补充 ignore-update-only-columns 过滤器说明这一主要变更。
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

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• Create PR with unit tests
• Commit unit tests in branch cdc/add-ignore-config

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📥 Commits

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📒 Files selected for processing (3)

• ticdc/ticdc-changefeed-config.md
• ticdc/ticdc-filter.md
• ticdc/ticdc-open-api-v2.md

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