Get GUI settings from API

As seen in the process of containerizing the GUI, it might be necessary to create a way to get GUI settings from the API instead of using the ones in env variables during the build which cannot be modified later.

This will make the GUI more flexible to be used inside a container without having to build every time a setting needs to be changed. Also, it will be nice to not remove the previous way to do the setup (on build) just to avoid possible retro compatibility issues