KubernetesClientBuilder enhancements for common HttpClient customizations

[shawkins]

    > First of all, I should not have to create Kubernetes client first so that I can get http client builder to replace interceptor and then get http client factory and finally create Kubernetes clients from builder using that http client factory. This is pretty messy builder pattern implementation from API point of view.

That's obviously not intended. There are really two issues here. The first is that there's no current way exposed for getting the default HttpClient Factory. A method for that can easily be extracted from HttpClientUtils.createHttpClient. The second is that the factory logic assumes customization via sub-classing (see the XXXClientFactory.additionalConfig methods). There wasn't a mechanism envisioned for modifying across any factory - such as modifying the interceptors in a common way.

Why not pass HttpClientBuilder or HttpClientFactoryBuilder to KubernetesClientBuilder?

Since we added HttpClient.getFactory, HttpClient.Builder is viable as a possible argument to KubernetesClientBuilder. To fully decompose it's also possible to change HttpClient.Factory.createHttpClient(Config config) to be HttpClient.Factory.processConfig(Config config, HttpClient.Builder).

That looks approximately like:

HttpClient.Factory factory = HttpClient.Factory.new();
HttpClient.Builder builder = factory.newBuilder();
// make modifications that could be overridden by processing the config
factory.processConfig(config, builder);
// make modifications that override the config
builder.addOrReplaceInterceptor ...
// then supply the builder to the KubernetesClientBuilder

However it's also possible to just associate a Consumer<HttpClient.Builder> with the KubernetesClientBuilder:

new KubernetesClientBuilder()
  .withConfig(config)
  .withAdditionalHttpClientConfiguration(b -> b.addOrReplaceInterceptor... )
  .build();

That eliminates a few of the steps.

Originally posted by @shawkins in #2271 (comment)