message: config: add missing methods to Config type
diff: @@ -30,10 +30,12 @@ export type AppConfig = {
  };
  export type Config = {
  + has(key: string): boolean;
  +
  keys(): string[];
  - get(key: string): JsonValue;
  - getOptional(key: string): JsonValue | undefined;
  + get(key?: string): JsonValue;
  + getOptional(key?: string): JsonValue | undefined;
  getConfig(key: string): Config;
  getOptionalConfig(key: string): Config | undefined;
  