symmetry in the way we specify request factories

[joshlong]

    @Bean
    JdkClientHttpRequestFactory jdkClientHttpRequestFactory() {
        return new JdkClientHttpRequestFactory();
    }

    @Bean
    RestClient restClient(
            JdkClientHttpRequestFactory jdkClientHttpRequestFactory,
            RestClient.Builder builder) {
        return builder
                .requestFactory(jdkClientHttpRequestFactory)
                .build();
    }

    @Bean
    RestTemplate restTemplate(
            JdkClientHttpRequestFactory jdkClientHttpRequestFactory,
            RestTemplateBuilder builder) {
        return builder
                .requestFactory(() -> jdkClientHttpRequestFactory)
                .build();
    }

it would be nice if the ResstClient also took a Supplier<T> and the RestTemplate took a reference.