With Angular 7, when you create an app with the default app generator,
it creates two basic environment files: development and production.
When you run ng serve it serves with the development environment settings.
To build production you run ng build --prod.
My problem was that I wanted more environments, particularly,
a local, development, and production environment. So I wanted to add
a new settings file for local work and have ng serve use the local settings.
This will look at how to create additional environment settings files,
how to use ng build with your custom environment, and how to use
ng serve with the custom environments too.
The serve command first calls build, so we will first look at how to update
the build step and then the serve action.