bug: failed to reply RPC_EXTRA_INFO：the max length of data is 16777215 but got 127305012

### Current Behavior

This Error occurs:
```
2023/02/01` 07:18:32 [error] 50#50: *205966883 [lua] init.lua:841: phase_func(): failed to reply RPC_EXTRA_INFO: the max length of data is 16777215 but got 127305012, client: 172.30.65.0, server: _, request: "POST /oam/2.0/tenant/import/agent HTTP/1.1", host: "192.168.60.21", referrer: "http://192.168.60.21:32004/"
2023/02/01 07:18:32 [warn] 50#50: *205966883 [lua] plugin.lua:901: run_plugin(): ext-plugin-pre-req exits with http status code 503, client: 172.30.65.0, server: _, request: "POST /oam/2.0/tenant/import/agent HTTP/1.1", host: "192.168.60.21", referrer: "http://192.168.60.21:32004/"
172.30.65.0 - - [01/Feb/2023:07:18:32 +0000] 192.168.60.21 "POST /oam/2.0/tenant/import/agent HTTP/1.1" 503 671 1.215 "http://192.168.60.21:32004/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.88 Safari/537.36" - - - "http://192.168.60.21"
```
Source code location:
`https://github.com/apache/apisix/blob/master/apisix/plugins/ext-plugin/init.lua`

### Expected Behavior

This is the MAX_ DATA_ SIZE become a configurable variable.

### Error Logs

2023/02/01 07:18:32 [error] 50#50: *205966883 [lua] init.lua:841: phase_func(): failed to reply RPC_EXTRA_INFO: the max length of data is 16777215 but got 127305012, client: 172.30.65.0, server: _, request: "POST /oam/2.0/tenant/import/agent HTTP/1.1", host: "192.168.60.21", referrer: "http://192.168.60.21:32004/"
2023/02/01 07:18:32 [warn] 50#50: *205966883 [lua] plugin.lua:901: run_plugin(): ext-plugin-pre-req exits with http status code 503, client: 172.30.65.0, server: _, request: "POST /oam/2.0/tenant/import/agent HTTP/1.1", host: "192.168.60.21", referrer: "http://192.168.60.21:32004/"
172.30.65.0 - - [01/Feb/2023:07:18:32 +0000] 192.168.60.21 "POST /oam/2.0/tenant/import/agent HTTP/1.1" 503 671 1.215 "http://192.168.60.21:32004/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.88 Safari/537.36" - - - "http://192.168.60.21"

### Steps to Reproduce

Use the ext-plugin-pre-req plugin,Upload large data content.

### Environment

- APISIX version (run `apisix version`): 3.1.0
- Operating system (run `uname -a`): Linux apisix-5f5f44c88-ck2jr 3.10.0-862.el7.x86_64
- OpenResty / Nginx version (run `openresty -V` or `nginx -V`): openresty/1.21.4.1
- etcd version, if relevant (run `curl http://127.0.0.1:9090/v1/server_info`):
- APISIX Dashboard version, if relevant:
- Plugin runner version, for issues related to plugin runners:
- LuaRocks version, for installation issues (run `luarocks --version`):