title: Configure ServiceCollection via JSON file
body: <p>Is there an example of configuring dependency injection in .NET Core 2.0 via a JSON file that would contain <em>interface -> class mappings</em>? E.g.</p>
  
  <pre><code>var someServiceConfigBuilder = new ConfigurationBuilder();
  someServiceConfigBuilder.AddJsonFile("someservice.json");
  var someServiceConfig = someServiceConfigBuilder.Build();
  
  var services = new ServiceCollection();
  services.AddOptions();
  services.Configure&lt;SomeServiceOptions&gt;(someServiceConfig);
  services
      // TODO this should really come from the JSON config file
      .AddTransient&lt;ISomeService, SomeService&gt;();
  </code></pre>
  
  <p>So rather than hard-coding the mappings with calls to <code>AddTransient()</code>, it'd be great to have this info coming from the JSON file.</p>
  
  <p>Is this supported? If yes, what's the expected format of the JSON config?</p>