Add forRootAsync for configuration via configService

[DimosthenisK]

I'm submitting a...

[ ] Regression 
[ ] Bug report
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

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

Nest version: 6.6.0

 
For Tooling issues:
- Node version: 12  
- Platform: Windows 

Others:

[DimosthenisK]

Hey, just for a notice, I went ahead and bypassed this.
I created a wrapper module, and I instanciate the DynamicModule from it.

import * as azure from '@nestjs/azure-storage';

export const AZURE_STORAGE_MODULE_OPTIONS = azure.AZURE_STORAGE_MODULE_OPTIONS;

@Module({
    providers: [
        azure.AzureMulterStorageService,
        azure.AzureStorageService,
    ],
    exports: [
        azure.AzureMulterStorageService,
        azure.AzureStorageService,
        azure.AZURE_STORAGE_MODULE_OPTIONS,
    ],
})
export class AzureModule {
    static withConfig(
        optionsProvider: Provider<azure.AzureStorageOptions>
    ): DynamicModule {
        return {
            module: AzureModule,
            providers: [optionsProvider],
        };
    }
}

[manekinekko]

Interesting. Thanks for sharing.

[ksivamuthu]

@manekinekko I've added PR to this issue. Please review and let me know your suggestions.