Make "right-derive-when-split" description more clear

[lilin90]

What is changed, added or deleted? (Required)

The description for the right-derive-when-split TiKV config item is not clear, not easy to understand. This PRs makes the description more clear. The description in English docs is clear: https://docs.pingcap.com/tidb/stable/tikv-configuration-file#right-derive-when-split

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 (in Chinese).

• master (the latest development version)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v8.0 (TiDB 8.0 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)

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

• This PR is translated from:
• Other reference link(s): https://docs.pingcap.com/tidb/stable/tikv-configuration-file#right-derive-when-split

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

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-28 07:29:59.483450333 +0000 UTC m=+941794.617900446: ☑️ agreed by 3pointer.
• 2024-08-28 07:55:34.637013983 +0000 UTC m=+943329.771464105: ☑️ agreed by qiancai.

[lilin90]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lilin90

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #18479.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #18480.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.2: #18481.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.2: #18482.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.3: #18483.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #18484.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #18485.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.4: #18486.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #18487.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.0: #18488.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.3: #18489.