v8.5.5: ticdc: add header line for CSV protocol (#21417)

[ti-chi-bot]

This is an automated cherry-pick of #21417

First-time contributors' checklist

• [x] I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

1. Add a new field output-field-header
2. Add the header description about CSV protocol

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions (in Chinese).

• [x] master (the latest development version)
• [x] v9.0 (TiDB 9.0 versions)
• [ ] v8.5 (TiDB 8.5 versions)
• [ ] v8.4 (TiDB 8.4 versions)
• [ ] v8.3 (TiDB 8.3 versions)
• [ ] v8.1 (TiDB 8.1 versions)
• [ ] v7.5 (TiDB 7.5 versions)
• [ ] v7.1 (TiDB 7.1 versions)
• [ ] v6.5 (TiDB 6.5 versions)
• [ ] v6.1 (TiDB 6.1 versions)
• [ ] v5.4 (TiDB 5.4 versions)

What is the related PR or file link(s)?

• This PR is translated from: https://github.com/pingcap/docs-cn/pull/20478
• Other reference link(s): https://github.com/pingcap/tiflow/pull/12183

Do your changes match any of the following descriptions?

• [ ] Delete files
• [ ] Change aliases
• [ ] Need modification after applied to another branch
• [ ] Might cause conflicts after applied to another branch

[gemini-code-assist[bot]]

Summary of Changes

Hello @ti-chi-bot, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the TiCDC documentation for the CSV protocol by introducing a new configuration option, output-field-header. This enhancement allows users to generate CSV files with a descriptive header row, significantly improving the clarity and usability of the output data for downstream processing and analysis. The changes include adding the configuration to the example, detailing the header structure, and providing a concrete output example.

Highlights

• New Configuration Option: Introduced the output-field-header configuration parameter for the CSV protocol, allowing users to control the inclusion of a header row in the output. This option is new in v9.0.0 and defaults to false.
• CSV Header Documentation: Added detailed documentation explaining the structure and content of the CSV header row when output-field-header is set to true, including a table mapping column numbers to their respective header names.
• CSV Output Example: Provided a new example demonstrating the CSV output format when the header row is enabled, showcasing how metadata columns and data change columns are represented.

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