Add different configuration settings for different environments

[lecaillon]

Motivation:

Actually Evolve does not support different configuration for different environments for .NET Core projects.
It only uses a simple json file called Evolve.js for it.
Not ideal when you want to have different setup between Development, Staging and Production.

Solution:

Allow to specfiy multiple configuration files merged at build-time by Evolve depending the selected build configuration. A little like the appsettings.json file behavior.

Exemple:

2 configurations files:

• Evolve.js
• Evolve.Staging.js

Assuming you've created a specfic build configuration called Staging, the result will be:

• In Debug configuration mode, only the Evolve.js file is loaded by Evolve.
• In Staging configuration mode, the Evolve.js file will be loaded first and then, will be overriden by the Evolve.Staging.js file.