[WIP]: add v8.5.4 release notes

[qiancai]

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[gemini-code-assist]

Summary of Changes

Hello @qiancai, I'm Gemini Code Assist¹! 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 introduces the official release notes for TiDB 8.5.4. The new documentation outlines compatibility changes, various improvements across TiDB, TiKV, PD, and related tools, as well as critical bug fixes. The PR is currently marked as a Work In Progress, indicating further content or review might be needed before finalization.

Highlights

• New Release Notes Added: A new Markdown file, releases/release-8.5.4.md, has been added to document the release notes for TiDB version 8.5.4.
• Compatibility Changes: The release notes include a significant compatibility change in TiKV, deprecating several region-compact configuration items and replacing them with a new gc.auto-compaction configuration group for better control over automatic compaction behavior.
• Improvements: Key improvements highlighted include support for creating global indexes on non-unique columns of partitioned tables in TiDB, the ability to apply the semi_join_rewrite hint to Semi Joins in IN subqueries, optimization of tail latency for async snapshot and write operations in TiKV, and a reduction of unnecessary error logs in PD.
• Bug Fixes: Notable bug fixes address issues such as significantly overestimated row count estimates across months or years in TiDB and an improper initialization of the PD client retry policy.

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[gemini-code-assist]

Code Review

This pull request adds the release notes for TiDB v8.5.4. The file appears to be a work in progress, containing several placeholders and entries with internal duplication markers. My review focuses on cleaning up these entries to align with the documentation style, updating outdated links, and removing placeholders. I've provided specific suggestions for each duplicated entry to make them ready for the final version. Also, please ensure the file ends with a newline character for consistency.

[qiancai]

v8.5.3 already includes the following issue for tikv/tikv#18615. Now in v8.5.4, there is another PR tikv/tikv#18783 for the same issue. Should we use the same release note in v8.5.4?

Fix the issue that log backup uploads to Azure Blob Storage are slow when transferring large volumes of data #18410 @YuJuncen

[qiancai]

v8.5.3 already includes the following issue for pingcap/tidb#62232. Now in v8.5.4, there is another PR pingcap/tidb#63485 for the same issue. Should we use the same release note in v8.5.4?

- Add flow control interfaces for Region splitting and data ingestion during data import [#61553](https://github.com/pingcap/tidb/issues/61553) @[tangenta](https://github.com/tangenta)

[qiancai]

v8.5.3 already includes the following issue for pingcap/tidb#62232. Now in v8.5.4, there is another PR tikv/tikv#18581 for the same issue. Should we use the same release note in v8.5.4?

- Optimize the handling of `CompactedEvent` in Raftstore by moving it to the `split-check` worker, reducing blocking on the main Raftstore thread [#18532](https://github.com/tikv/tikv/issues/18532) @[LykxSassinator](https://github.com/LykxSassinator)

[YuJuncen]

• Fix the issue where Zstd compression did not take effect in log backup, resulting in uncompressed output. #18836 @3pointer
• Fixed a bug that may cause flush operation slow in azure blob storage. #18410 @YuJuncen
• Fixed a bug that may cause log truncate panic when failed to delete file. #63358 @YuJuncen
• Fixed a bug that may cause stats_meta be zero when checksumming disabled. #60978 @Leavrth
• Reduced chance of BR restore failure from S3-compatible storage when the S3 server limits bandwidth through traffic shaping. #18846 @kennytm
• Fix the issue that the log backup observer loses observation of a region. #18243 @Leavrth
• Fixed a a bug that may cause restore point fail when there are some special sized table schemas. #63663 @RidRisR