Add support of asynchronous registration for module

[thomasdom]

Currently, this module does not support async registration.

Async registration would be useful for getting configuration variables from ConfigModule, among many other use cases.

We should be able to register the module like this:

MeiliSearchModule.forRootAsync({
  imports: [ConfigModule],
  inject: [ConfigService],
  useFactory: (configService: ConfigService) => ({
    host: configService.get<string>('MEILISEARCH_HOST'),
    apiKey: configService.get<string>('MEILISEARCH_API_KEY'),
  }),
}),

[thomasdom]

@lambrohan Do you still maintain this repository?

[lambrohan]

@thomasdom Yes. I'll add the async registration support very soon.

[lambrohan]

@thomasdom Just did the update. It should support async module registration now.