default WebClientRequestPreparation prepare() {
        return new WebClientRequestPreparation(this);
    }
Prepares to send an {@link HttpRequest} using fluent builder.
<pre>{@code
WebClient client = WebClient.of(...);
HttpResponse response = client.prepare()
                              .post("/foo")
                              .header(HttpHeaderNames.AUTHORIZATION, ...)
                              .content(MediaType.JSON, ...)
                              .execute();
}</pre>
core/src/main/java/com/linecorp/armeria/client/WebClient.java