Separate out the App.config and settings.json functionality into a separate assembly

[Anash P. Oommen]

The library can mostly be used without an App.config and settings.json. But working with Microsoft.Extensions.* dependencies is a pain.

Let's separate out configuration functionality (through environment variables, json and config files) into a separate extensions library, so that

• Core library can be used as is (users can configure the library at runtime)
• Those who want configuration through files can add additional assembly dependency.
• We have a place to add more platform-specific functionality in the future. For instance, I really want to pull in #484, but that functionality is largely irrelevant for those who don't use DI and ASP.NET Core.

Some relevant bugs that made me think this way:

• #476
• #491
• #483

[Anash P. Oommen]

Fixed in v16.0.0.

[sommmen]

Hiya @AnashOommen - what would be the recommended way to register the GoogleAdsConfig now? I just updated and it seems GoogleAdsConfig no longer can take a Config;