Issue description

Add a request_body switch to the schema, and each body can be used by expr to decide whether to log or not. Without this switch, the body is not logged.

"kafka-logger": {
   "broker_list":{
       "127.0.0.1":9092
    },
   "kafka_topic" : "test2",
   "request_body": {
       "expr": [
          ["request_length", "<", "1024"],
       ]
   },
   "key" : "key1",
   "batch_max_size": 1,
   "name": "kafka logger"
}

expr can be evaluated by lua-resty-expr. request body can be fetched by core.request.get_body.

Environment

• apisix version (cmd: apisix version): 2.10.1
• OS (cmd: uname -a):
• OpenResty / Nginx version (cmd: nginx -V or openresty -V):
• etcd version, if have (cmd: run curl http://127.0.0.1:9090/v1/server_info to get the info from server-info API):
• apisix-dashboard version, if have:
• the plugin runner version, if the issue is about a plugin runner (cmd: depended on the kind of runner):
• luarocks version, if the issue is about installation (cmd: luarocks --version):