doc: add dubbo-go-extensions in readme

[zbchi]

Description

#3242
add dubbo-go-extensions in readme

Checklist

• I confirm the target branch is develop
• Code has passed local testing
• I have added tests that prove my fix is effective or that my feature works

[zbchi]

@AlexStocks @Alanxtl first draft. need comments and revisions

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.14%. Comparing base (60d1c2a) to head (d061f91).
⚠️ Report is 757 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3260      +/-   ##
===========================================
+ Coverage    46.76%   48.14%   +1.37%     
===========================================
  Files          295      466     +171     
  Lines        17172    34043   +16871     
===========================================
+ Hits          8031    16390    +8359     
- Misses        8287    16322    +8035     
- Partials       854     1331     +477     

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[Copilot]

Pull request overview

This PR updates the project documentation to surface the new apache/dubbo-go-extensions repository as part of Dubbo-go’s ecosystem, aligning with Issue #3242’s request to update README materials.

Changes:

• Add an “Extensions / 扩展生态” section linking to dubbo-go-extensions and describing its purpose.
• Add dubbo-go-extensions to the “Ecosystem / 生态系统” lists in both English and Chinese READMEs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
README.md	Adds an Extensions section and ecosystem entry pointing to apache/dubbo-go-extensions.
README_CN.md	Adds a corresponding 扩展生态 section and ecosystem entry pointing to apache/dubbo-go-extensions.

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[AlexStocks]

文档结构和内容有几个问题，详见各文件的行内评论。

[AlexStocks]

上次提的三个问题（独立 section 头重脚轻、描述信息密度低、Ecosystem 列表顺序）还没有回应，也没有新的提交。请先处理一下之前的 review 意见。

[Alanxtl]

另外 工具生态 这一栏顺便改一下，就是每个工具一行介绍就行了，现在占的篇幅有点大

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Alanxtl]

lgtm