*: add notice on flashback cluster usage

[BornChanger]

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[BornChanger]

/cc @cfzjywxk

[ti-chi-bot[bot]]

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-03-13 06:34:09.635623624 +0000 UTC m=+840076.657870022: :ballot_box_with_check: agreed by qiancai.
• 2024-03-13 08:00:24.274188213 +0000 UTC m=+845251.296434601: :ballot_box_with_check: agreed by Oreoxmt.

[qiancai]

/approve

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #16831.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #16832.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #16833.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.6: #16834.