add body_filter_by_lua_block lua plugin to ingress-nginx

rootfs/etc/nginx/lua/plugins/README.md

@@ -15,6 +15,7 @@ By defining functions with the following names, you can run your custom Lua code
  - `init_worker`: useful for initializing some data per Nginx worker process
  - `rewrite`: useful for modifying request, changing headers, redirection, dropping request, doing authentication etc
  - `header_filter`: this is called when backend response header is received, it is useful for modifying response headers
+ - `body_filter`: this is called when response body is received, it is full for logging response body 
  - `log`: this is called when request processing is completed and a response is delivered to the client
 
 Check this [`hello_world`](https://github.com/kubernetes/ingress-nginx/tree/master/rootfs/etc/nginx/lua/plugins/hello_world) plugin as a simple example or refer to [OpenID Connect integration](https://github.com/ElvinEfendi/ingress-nginx-openidc/tree/master/rootfs/etc/nginx/lua/plugins/openidc) for more advanced usage.

rootfs/etc/nginx/template/nginx.tmpl

@@ -1112,6 +1112,7 @@ stream {
             }
 
             body_filter_by_lua_block {
+                plugins.run()
             }
 
             log_by_lua_block {