ticdc: fix the description of safe-mode (#13792)

[ti-chi-bot]

This is an automated cherry-pick of #13792

What is changed, added or deleted? (Required)

Fix an inconsistency issue in the TiCDC FAQ by updating the description from if I set enable-old-value to true to if I set safe-mode to true. The following content of this FAQ is focused on the safe-mode feature rather than enable-old-value.

TiCDC guarantees that all data is replicated at least once. When there is duplicate data in the downstream, write conflicts occur. To avoid this problem, TiCDC converts `INSERT` and `UPDATE` statements into `REPLACE INTO` statements. This behavior is controlled by the `safe-mode` parameter.

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.

• master (the latest development version)
• v7.1 (TiDB 7.1 versions)
• v7.0 (TiDB 7.0 versions)
• v6.6 (TiDB 6.6 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

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

• This PR is translated from: ticdc: fix the description of safe-mode docs#13337
• Other reference link(s):

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

[ti-chi-bot]

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[Oreoxmt]

/merge

[ti-chi-bot]

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

Commit hash: 5fd4375