Update complex-cdc.yaml

[asddongmen]

Add gc-ttl config example in cdc_servers config.
#1961

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[TomShawn]

LGTM

[TomShawn]

/merge

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

Commit hash: b997030

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #6676.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #6677.