DataLoader Dependency Injection Support

[michaelstaib]

The DataLoader could already resolve dependencies from the dependency injection container. With this change it is now possible to register a DataLoader with the standard dependency injection container. This enables referencing DataLoaders through interfaces.

Here is how we can now register a DataLoader:

services.AddDataLoader<IMyDataLoader, MyDataLoader>();

services.AddDataLoader<MyDataLoader>();

services.AddDataLoader<IMyDataLoader>(s => ....);

The DataLoaderRegistry is automatically registered when using this.

On the resolver side I can now resolve my DataLoader through an interface:

public async Task<string> ResolveSomething(IMyDataLoader dataLoader) 
{

}

I also do not need to use the [DataLoader] attribute I the interface implements IDataLoader.

Fixes #926