adopters: add kunlun case study (#5019)

[ti-srebot]

cherry-pick #5019 to release-2.1
You can switch your code base to this Pull Request by using git-extras:

# In docs repo:
git pr https://github.com/pingcap/docs/pull/5021

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/docs.git pr/5021:release-2.1-4d2a21935d3c

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Signed-off-by: Ran huangran@pingcap.com

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[ti-srebot]

@ran-huang you're already a collaborator in bot's repo.

[ran-huang]

/lgtm
/merge

[ti-chi-bot]

@ran-huang: /merge in this pull request requires 1 /lgtm.

In response to this:

/lgtm
/merge

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[ti-chi-bot]

[REVIEW NOTIFICATION]

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• ran-huang

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[ran-huang]

/merge

[ti-chi-bot]

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

Commit hash: aead2d5