ticdc: add example of how to show bdr role

[asddongmen]

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Timeline:

• 2024-01-29 02:20:13.543837014 +0000 UTC m=+1359255.108134716: ☑️ agreed by qiancai.

[qiancai]

/test pull-verify

[qiancai]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.6: #16394.