Provide a lightweight and simple way to configure SDK

[RomanReznichenko]

The SDK should provide a convenient way to be configured. The configuration could be passed into the client constructors. However, the configuration must be a single instance to coordinate settings across the whole library.

class Configuration {
  get container(): DependencyContainer {
    return container;
  }

  constructor() {
    this.container.register(
      Configuration,
      { useValue: this }
    );
  }
  
  // implementation
}

const configuration = new Configuration();
const configuration2 = container.resolve(Configuration);

expect(configuration2).toBe(configuration);

The configuration should use a certain number of credential providers to obtain credentials from different sources such as rc dotfiles and environment variables:

export interface Credentials {
  readonly id: string;
  readonly token: string;
}

export interface CredentialProvider {
  get(): Promise<Credentials | undefined>;
}

However, it should preserve the ability to pass an instance of Credentials manually:

class Configuration {
 constrcutor(options: { 
   // ...
   credentials?: Credentials;
   credentialProviders?: CredentialProvider[];
 }) {}
}

While using rc dotfile it should perform JSON schema validation to throw an exception if the config doesn't meet certain validation rules. It also might be helpful when we decide to provide autocomplete while using IDE or any other editor like VSCode.

Finally, the configuration should obtain the SDK version and expose this information to the client in some way. Depending on the build process we can inline this information while bundling source files or read it from the package.json.