Possibility to reload "max_memory_restart" without restarting apps

[endel]

Hi @Unitech, I hope you are doing great!

Would you consider merging if I can introduce a PR allowing to update the max_memory_restart config at runtime, without restarts?

CLI usage suggestions:

• pm2 reload-config ecosystem.config.js
• pm2 hot-reload ecosystem.config.js

(The "hot-reload" command name may leave users wanting an actual hot reloading of the entire application - which MAY be possible to achieve eventually. But this is not the intent of the PR.)

Kind regards, Endel