Change the priority of the configuration:
1. If it is a new installation of EMQX, the priority of configuration is `ENV > emqx.conf > HTTP API`.
2. If EMQX is upgraded from an old version (i.e., the cluster-override.conf file still exists in EMQX's data directory), then the configuration priority remains the same as before. That is, `HTTP API > ENV > emqx.conf`.

Deprecated data/configs/local-override.conf.

Stabilizing the HTTP API for hot updates.