Allow restricting custom origin error HTML to GET requests so other
methods pass through origin responses. Adds option seed, snapshot field,
edge limit_except/Lua handling, and admin UI switch.
- 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.
ryan