raft-engine: reduce the threshold of compression and add related metrics on it. (#16906)

[ti-chi-bot]

This is an automated cherry-pick of #16906

What is changed and how it works?

Issue Number: Ref #16907 ref tikv/raft-engine#358

What's Changed:

This pr contains:
- Reduce the default compression threshold in RaftEngine to `4kb` as default if users do not manually set it.
- Add relevant metrics on the compression ratio of RaftEngine.write.

The relevant metrics will be shown just like the following shows:

And as for performance, taking tpcc workloads, using v7.5.x (disable async-io and compression-threshold = 8kb as default) as the baseline, the CPU.utilization keeps nearly same in this pr.

And using smaller compression threshold with batch-compression-threshold = 4kb, async-io, keeps the same, and the costs of IO Bandwidth are smaller than v8.1.0-nightly ((batch-compression-threshold = 8kb, async-io). (PS: smaller is better in "Disk IO Throughputs")

QPS Diff	Disk IO Throughputs

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Release note

For the version of TIKV >= v8.1:
- Reduce the default compression threshold in RaftEngine to `4kb` as default if users do not manually set it.
- Add relevant metrics on the compression ratio of RaftEngine.write.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• LykxSassinator
• glorv

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[glorv]

/merge

[ti-chi-bot]

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

Commit hash: afdd2a6