[FEATURE] add OPA on pixiu-admin

[AlexStocks]

✅ 验证清单

• 🔍 我已经搜索过 现有 Issues，确信这不是重复请求
• 📋 我已经查看了 发布说明，确信此功能尚未实现

🎯 功能描述

在 pixiu-admin 上配置 OPA 的配置

📋 使用场景

动态允许或者拒绝某个路径

⚖️ 复杂性与风险评估

No response

🔗 外部依赖

No response

📚 附加信息

No response

[AlexStocks]

@nanjiek

[1kasa]

@sirui

[Alanxtl]

#843
#822
#751
#732

[nanjiek]

PR Breakdown for the Issue

This issue will be completed by splitting it into three pull requests (PRs):

PR1 (Backend: Admin OPA Configuration)

Content: Implement CRUD/publishing interfaces in admin/controller/…, admin/logic/… and router.go; configure etcd paths and perform validation; integrate Swagger and synchronize documents; write unit tests/integration tests (with mocked etcd).

PR2 (E2E Full-Link Verification)

Content: Develop end-to-end test cases (covering allow/deny scenarios) for the entire process of admin configuration -> gateway loading -> OPA decision-making, including relevant scripts and documentation; reuse the existing gateway OPA implementation (PR2 has been completed).
Dependency: This PR can only be started after PR1 is merged.

Frontend PR (OPA Configuration Management UI)

Content: Configure menus/routes; add a new OPA page (referencing the style of RateLimiter/Plug, supporting YAML editing/saving/deletion/publishing); conduct frontend self-tests or lightweight E2E tests (with mocked APIs).
Dependency: This PR can be developed in parallel after the backend API paths in PR1 are finalized.