Add info to PREPARE statement docs

[Oreoxmt]

First-time contributors' checklist

What is changed, added or deleted? (Required)

Add information about some limits

See also: https://github.com/pingcap/tidb/blob/cfbabfa705dbbc97c8e1e00af7f2d2620406304c/pkg/planner/core/plan_cache_utils.go#L101-L105

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• [x] master (the latest development version)
• [x] v8.1 (TiDB 8.1 versions)
• [x] v8.0 (TiDB 8.0 versions)
• [ ] v7.6 (TiDB 7.6 versions)
• [ ] v7.5 (TiDB 7.5 versions)
• [ ] v7.1 (TiDB 7.1 versions)
• [ ] v6.5 (TiDB 6.5 versions)
• [ ] v6.1 (TiDB 6.1 versions)
• [ ] v5.4 (TiDB 5.4 versions)
• [ ] v5.3 (TiDB 5.3 versions)
• [ ] v5.2 (TiDB 5.2 versions)
• [ ] v5.1 (TiDB 5.1 versions)

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

• This PR is translated from: https://github.com/pingcap/docs/pull/17309
• Other reference link(s):

Do your changes match any of the following descriptions?

• [ ] Delete files
• [ ] Change aliases
• [ ] Need modification after applied to another branch
• [ ] Might cause conflicts after applied to another branch

[Oreoxmt]

/cc @hawkingrei

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-05-20 05:31:48.078517324 +0000 UTC m=+2063261.835652893: :ballot_box_with_check: agreed by qiancai.

[Oreoxmt]

/approve

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Oreoxmt

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• ~~OWNERS~~ [Oreoxmt]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.0: #17377.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #17378.