补充：ngx.exit 接口使用说明

[Miss-you]

1. ngx.exit 是什么？有什么用？
2. 结合案例进一步理解ngx.exit退出阶段的含义

ref:
apache/apisix#2703

another ref：
https://github.com/openresty/lua-nginx-module#ngxexit

When status >= 200 (i.e., ngx.HTTP_OK and above), it will interrupt the execution of the current request and return status code to Nginx.

When status == 0 (i.e., ngx.OK), it will only quit the current phase handler (or the content handler if the content_by_lua* directive is used) and continue to run later phases (if any) for the current request.