NGX_UI_LOADER_CONFIG_TOKEN not exported as public

[sgtonion]

Describe the bug
NGX_UI_LOADER_CONFIG_TOKEN is not exported.

1. This prevents user to feed configurations for the loader using Dependency Injection
2. The NgxUiLoaderService does not currently handle Promise type values as configuration which would prevent the configuration to be set

Expected behaviour
adding in AppModule's provider: [{ provide: NGX_UI_LOADER_CONFIG_TOKEN, useFactory: callServerToGetConfiguration, deps: [HttpClient] }]

allows service to read the configuration from callServerToGetConfiguration and then apply to the ngx-loader