How are quick actions processed and can those be hooked?

Hi everyone,

I need to check if an available on-prem GitLab instance used by developers can be integrated with some 3rd party app and already read a lot about different kinds of hooks and events, especially WebHooks. Though, I don’t came across how quick actions work and if there’s some underlying hook mechanism as well, which might be enhanced to use custom quick actions and stuff.

So, how are things like /cc, /approve etc. handled by GitLab itself internally? Is there some way to trigger custom code whenever such a quick action is written in issues? Is there some way to register custom quick actions like /custom_prefix_do_something_really_custom ...and support some payload as well!?