configure abstract method

Applies additional configuration to the HttpMessageHandlerBuilder.

The next parameter represents the next filter in the pipeline, or the final handler building step if this is the last filter.

Filters can execute code before and after calling next:

class MyFilter extends HttpMessageHandlerBuilderFilter {
  @override
  void configure(
    void Function(HttpMessageHandlerBuilder) next,
    HttpMessageHandlerBuilder builder,
  ) {
    // Execute code before building
    print('Building handler for: ${builder.name}');

    // Call the next filter in the pipeline
    next(builder);

    // Execute code after building
    print('Handler built for: ${builder.name}');
  }
}