dumpling: merge userguide into docs

[hfxsd]

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

• This PR is translated from:dumpling: merge userguide into docs docs#19890
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• Delete files
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[qiancai]

Rest LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-17 09:56:14.37088147 +0000 UTC m=+285245.825927613: ☑️ agreed by lance6716.
• 2025-01-20 03:59:14.852231659 +0000 UTC m=+66882.183151065: ☑️ agreed by qiancai.

[hfxsd]

/approve

[ti-chi-bot]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #19592.