memleak in rest api

[OdyWayne]

Describe the bug
There will be memleaks using certain rest apis.

To Reproduce
Start NanoMQ with http server feature on; use mosquitto_sub to sub a topic; use rest api like "GET /api/v4/clients"; then you will get a memleak.
There are other rest apia can also cause memleak like "GET /api/v4/subscriptions/{clientid}", "GET /api/v4/subscriptions", "GET /api/v4/clients/username/{username}", "GET /api/v4/clients/{clientid}", "GET /api/v4/prometheus".

** Environment Details **

• NanoMQ version: latest main branch
• Operating system and version: Ubuntu 22.04

[OdyWayne]

fixed here --> #1455