[ISSUE #9004] docs: add nginx load balancing guide for Nacos cluster

[EvanYao826]

What does this PR do?

Closes #9004: Add official documentation for using Nginx as a load balancer for a Nacos cluster.

Problem

Many users need to use Nginx to load balance a Nacos cluster, but there was no official guide. Online tutorials are often incomplete — most miss the critical stream block for gRPC proxying, causing client connection failures.

Changes

Added doc/nginx-cluster-load-balance-guide.md covering:

• Why use Nginx instead of comma-separated server addresses
• Complete Nginx configuration for both HTTP (8848) and gRPC (9848) protocols
• Port mapping explanation (Nacos gRPC = HTTP port + 1000)
• Client configuration examples
• Troubleshooting common issues

The guide is based on the solution shared in the issue comments by the original reporter, enhanced with best practices and additional context.

Assisted-by: Hermes Agent

[github-actions]

Thanks for your this PR. 🙏
Please check again for your PR changes whether contains any usage/api/configuration change such as Add new API , Add new configuration, Change default value of configuration.
If so, please add or update documents(markdown type) in docs/next/ for repository nacos-group/nacos-group.github.io

---

感谢您提交的PR。 🙏
请再次查看您的PR内容，确认是否包含任何使用方式/API/配置参数的变更，如：新增API、新增配置参数、修改默认配置等操作。
如果是，请确保在提交之前，在仓库nacos-group/nacos-group.github.io中的docs/next/目录下添加或更新文档（markdown格式）。

[github-actions]

⚠️ Commit Author Verification Failed

The following commits have author emails not linked to any GitHub account.
This will prevent CLA signing and block your PR from being merged.

Commit	Author	Email
f750b9b	EvanYao826	evanyao826@gmail.com

How to fix:

1. Add your commit email to your GitHub account: https://github.com/settings/emails
2. Or update your local git config to use an email already linked to GitHub:

   git config user.name "Your GitHub Username"
   git config user.email "your-github-email@example.com"
   

3. Amend your commits and force-push:

   git rebase -i HEAD~1 # mark commits as "edit" and amend author
   git push --force-with-lease
   

This check will re-run automatically after you push.

[CLAassistant]

All committers have signed the CLA.

[EvanYao826]

I have read the CLA Document and I hereby sign the CLA

[KomachiSion]

please add document into nacos-group/nacos-group.github.io

[EvanYao826]

Got it, I will add the documentation to nacos-group/nacos-group.github.io and update this PR accordingly. Will follow up shortly.

[EvanYao826]

I have added the documentation to nacos-group/nacos-group.github.io:

nacos-group/nacos-group.github.io#1082

The guide is added under guide/admin/nginx-cluster-load-balance-guide.md in both English and Chinese versions.

[KomachiSion]

I have added the documentation to nacos-group/nacos-group.github.io:

nacos-group/nacos-group.github.io#1082

The guide is added under guide/admin/nginx-cluster-load-balance-guide.md in both English and Chinese versions.

Thanks, I will review in that PR.

[KomachiSion]

@EvanYao826 I reviewed with some comment in document PR.

[EvanYao826]

Closing this PR as the documentation has been moved to nacos-group/nacos-group.github.io#1082 per @KomachiSion's request.

The guide is now maintained in the documentation repository under guide/admin/nginx-cluster-load-balance-guide.md (both English and Chinese versions), updated for Nacos 3.x console port (8080).