feat(rate-limit): add default request rate limit configuration

- Support openresty_default_limit_req_per_ip in system_configs.
- Add limit_req and limit_req_status 429 directive generation in openresty renderer.
- Implement route-level limit_req_per_ip override and explicit disable.
- Add frontend UI inputs and validation in rate limits tab config.
- Update swagger API docs and changelog for v3.4.3-beta.3.

docs/swagger.yaml

@@ -2928,6 +2928,8 @@ definitions:
         type: integer
       limit_rate:
         type: string
+      limit_req_per_ip:
+        type: string
       origin_address:
         type: string
       origin_host:
@@ -3005,6 +3007,8 @@ definitions:
         type: integer
       limit_rate:
         type: string
+      limit_req_per_ip:
+        type: string
       origin_host:
         type: string
       origin_id:
@@ -7522,7 +7526,7 @@ paths:
         in: query
         name: hours
         type: integer
-      - description: 趋势桶分钟数（1、5 或 60，默认 60）
+      - description: 趋势桶分钟数（1、3、5 或 60，默认 60）
         in: query
         name: bucket_minutes
         type: integer