docs: fix TiKV RocksDB block-size defaults (#23269)

[ti-chi-bot]

This is an automated cherry-pick of #23269

What is changed, added or deleted? (Required)

Fixes the outdated default RocksDB block-size value in the following TiKV docs:

• storage-engine/rocksdb-overview.md
• tune-tikv-memory-performance.md

These documents said the default block size is 64 KB / 64KB, but the TiKV config template uses 32KB for rocksdb.defaultcf and rocksdb.writecf.

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.

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 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)

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/#block-size
  • https://raw.githubusercontent.com/tikv/tikv/master/etc/config-template.toml
  • https://raw.githubusercontent.com/tikv/tikv/release-8.5/etc/config-template.toml

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

[gemini-code-assist]

Code Review

This pull request updates the default RocksDB block size from 64 KB to 32 KiB in both the overview and memory performance tuning documentation. The reviewer suggested rephrasing a sentence in the overview document to improve clarity, simplicity, and readability, adhering to the repository style guide.

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[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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