Custom configuration keys in the angular portal

Hi, in v92 for the portal angular web project we need to create a new configuration key, not table related, not method related. Something like VI_Custom_Config_Key with a value. There are other oob keys created, we do not know where they get stored and they're not table/method related either , just as ServerConfig/ITShopConfig/InheritCategoryImagesToCategories of type boolean. How can we create one of our own?

Thanks!

Laura.