Better customization options for the underlying HTTP client

We're using the CF Java client under a fairly high load (tens of thousands of requests per day) and we would like to enable the metrics feature of reactor-netty, so that we can see how many connections are used at any point in time:

return createHttpClient().compress(true) // Code taken from _DefaultConnectionContext.java
            .tcpConfiguration(this::configureTcpClient)
            .secure(this::configureSsl)
            .metrics(true, new CustomHttpClientMetricsRecorder());

This is currently not possible unless we also override the entire reactor-netty client via DefaultConnectionContext.builder().httpClient(...), which we don't want to do, because it would involve to copy-pasting the entire HttpClient building logic from _DefaultConnectionContext. I could make a pull request that allows users of the CF Java client to do:

DefaultConnectionContext.builder()
    .metrics(true) // OR
    .metrics(true, new CustomHttpClientMetricsRecorder())
    .build();

But I also don't particularly like that idea, because this doesn't cover any future features that the rector-netty devs may implement (or already have implemented). Maybe something like the following would be best?

DefaultConnectionContext.builder()
    .additionalHttpClientConfiguration(httpClient -> httpClient.metrics(true) // OR
        .metrics(true, new CustomHttpClientMetricsRecorder()))
    .build();

What do you think?

Read _DefaultConnectionContext and the DefaultConnectionContext.builder entry point to understand how the reactor-netty HttpClient is assembled. Compare the proposed metrics options with the additionalHttpClientConfiguration hook, then identify existing client-building tests; done means callers can customize the underlying client without replacing the complete construction logic.