<fix>[loadBalancer]: block SLB deletion during grayscale upgrade

[zstack-robot-2]

Resolves: ZSTAC-78989

Target: 5.5.6

sync from gitlab !9187

[coderabbitai]

Walkthrough

在负载均衡器API拦截器中为APIDeleteLoadBalancerMsg消息添加了验证逻辑。新增的验证方法在启用灰度升级时，阻止删除独立SLB负载均衡器的操作。

Changes

Cohort / File(s)	Summary
负载均衡器验证逻辑 plugin/loadBalancer/src/main/java/org/zstack/network/service/lb/LoadBalancerApiInterceptor.java	在intercept方法中添加了对APIDeleteLoadBalancerMsg的处理分支，引入新的验证方法validate(APIDeleteLoadBalancerMsg msg)，在灰度升级场景下禁止删除独立SLB负载均衡器。

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 灰度升级时，负载均衡器需守护，
删除的请求在此处被拦截，
验证逻辑清晰如月光般明亮，
独立的SLB安然无恙，
代码简洁，意图鲜明！

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	标题遵循规定的格式 [scope]: ，长度为64个字符，符合72个字符的限制，并准确描述了主要变更内容：在灰度升级期间阻止SLB删除。
Description check	✅ Passed	描述与变更集相关，提供了JIRA工单号、目标版本和源同步信息，清晰地关联到负载均衡器组件中的SLB删除阻止功能。
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into 5.5.6

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch sync/ye.zou/fix/ZSTAC-78989

---

No actionable comments were generated in the recent review. 🎉

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}