Add forRootAsync for configuration via configService

I'm submitting a...

Current behavior

Currently, it's only possible to instantiate the module via the .withConfig method. It is not possible to inject a service into this method, so it is impossible to use a config service for the module instantiation.

Expected behavior

Enable both the .withConfig method and a factory-pattern method, that allows dependency injection.

What is the motivation / use case for changing the behavior?

I don't want to use process.env variables as all my config logic is inside a config module. It is possible to override this behavior by manually injecting all config values into process.env, but this seems like a bad choice.

Environment