planner: add docs for some variables

[qw4990]

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Oreoxmt
• TomShawn

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[TomShawn]

/cc @songrijie

[songrijie]

Others LGTM

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 676a4581b18bed0a45e65728928161ff4df06ce7

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10054.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10668.