pd: complement pd section

[qiancai]

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• This PR is translated from: pd: complement pd section docs-cn#20500
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• Delete files
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[qiancai]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #21211.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #21212.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #21213.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #21215.
But this PR has conflicts, please resolve them!