ticdc: update troubleshoot for ddl skip

[amyangfei]

First-time contributors' checklist

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

What is changed, added or deleted? (Required)

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

• master (the latest development version)
• v5.0 (TiDB 5.0 versions) Add troubleshooting info for ddl skip
• v4.0 (TiDB 4.0 versions) Add troubleshooting info for ddl skip
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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

ref: https://github.com/pingcap/ticdc/pull/1835

Add more instructions about how to find start-ts when cdc log doesn't contain it.

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

[amyangfei]

Suggested change

	2. 在 TiCDC log 中搜寻 `apply job` 字段，确认耗时较长的 DDL 的 `start-ts`。如果旧版本的 TiCDC 没有打印该 `start-ts`，可以查询 TiDB DDL history，找到该条 DDL 语句的 `binlog.TableInfo.update_timestamp` 字段，该字段即为所需的 `start-ts`。
	2. 在 TiCDC log 中搜寻 `apply job` 字段，确认耗时较长的 DDL 的 `start-ts`。如果旧版本（<= v4.0.13 或 <= v5.0.1）的 TiCDC 没有打印该 `start-ts`，可以查询 TiDB DDL history，找到该条 DDL 语句的 `binlog.TableInfo.update_timestamp` 字段，该字段即为所需的 `start-ts`。

[amyangfei]

PTAL @TomShawn

[TomShawn]

dev 版是最新开发版，应该不存在这个“旧版本”的历史问题。要不在 dev 中去掉“如果旧版本的 TiCDC 没有打印”这一句，在 release-x.0 文档中加上？

[amyangfei]

可以

[amyangfei]

ptal @TomShawn

[TomShawn]

LGTM

[ti-chi-bot]

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• TomShawn

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[TomShawn]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 46517fa

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #6334.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #6335.

[Joyinqin]

/translation done
/remove-translation doing

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/docs-cn#release-4.0 from head ti-chi-bot:cherry-pick-6331-to-release-4.0: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-6331-to-release-4.0."}],"documentation_url":"https://docs.github.com/rest/reference/pulls#create-a-pull-request"}