Add descriptions of new panels and update the plan cache doc

[TomShawn]

What is changed, added or deleted? (Required)

Add descriptions of new panels and update the plan cache doc

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

• This PR is translated from: Add descriptions of new panels and update the plan cache doc docs-cn#11799 planner: add description for plan cache variable docs-cn#11861
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• Delete files
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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hfxsd

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[TomShawn]

/cc @fzzf678

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[TomShawn]

Suggested change

	- This variable controls whether to count the memory consumed by the execution plans cached in the Prepared Plan Cache. When this switch is disabled, the memory usage displayed on the **Plan Cache Memory Usage** monitoring panel is 0. For details, see [Memory management of Prepared Plan Cache](/sql-prepared-plan-cache.md#memory-management-of-prepared-plan-cache).
	- This variable controls whether to count the memory consumed by the execution plans cached in the Prepared Plan Cache. For details, see [Memory management of Prepared Plan Cache](/sql-prepared-plan-cache.md#memory-management-of-prepared-plan-cache).

[hfxsd]

LGTM

[TomShawn]

/remove-status LGT1
/status LGT2

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 16dbc16