*: add slow log control variables (tidb_slow_log_rules, tidb_slow_log_max_per_sec) and hint write_slow_log

[lilin90]

What is changed, added or deleted? (Required)

https://github.com/pingcap/tidb/issues/64010

Add slow log control variables (tidb_slow_log_rules, tidb_slow_log_max_per_sec) and hint write_slow_log

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).

• [x] master (the latest development version)
• [x] v9.0 (TiDB 9.0 versions)
• [ ] v8.5 (TiDB 8.5 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)

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

• This PR is translated from: https://github.com/pingcap/docs-cn/pull/21009
• Other reference link(s): https://github.com/pingcap/tidb/issues/62959

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

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[gemini-code-assist[bot]]

Summary of Changes

Hello @lilin90, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request aims to enhance TiDB's slow log management capabilities. It introduces new system variables for fine-grained configuration of slow log rules and rate limiting, alongside a SQL hint to explicitly manage slow log recording for individual queries. This provides database administrators with improved tools for performance monitoring and debugging.

Highlights

• New Slow Log Control Variables: Introduces tidb_slow_log_rules and tidb_slow_log_max_per_sec to offer more precise control over slow log behavior and generation within TiDB.
• write_slow_log Hint: Adds a new hint, write_slow_log, enabling explicit control over whether a specific query's execution is recorded in the slow log.

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[lilin90]

I'll close this PR since the corresponding change is made in https://github.com/pingcap/docs/pull/22176.