Enhance #810 - multiple customization + `at()` method

[samchon]

export function SwaggerCustomizer(
  closure: (props: SwaggerCustomizer.IProps) => unknown,
): MethodDecorator;
export namespace SwaggerCustomizer {
  export interface IProps {
    swagger: ISwagger;
    method: string;
    path: string;
    route: ISwaggerRoute;
    at(func: Function): ISwaggerEndpoint | undefined;
    get(accessor: IAccessor): ISwaggerRoute | undefined;
  }
  export interface IAccessor {
    path: string;
    method: string;
  }
  export interface ISwaggerEndpoint extends IAccessor {
    route: ISwaggerRoute;
  }
}