@UnstableApi
    public TransformingRequestPreparation<AggregatedHttpResponse, ResponseEntity<String>> asString() {
        return as(AggregatedResponseAs.string());
    }
Converts the response content into {@link String}.
For example:
<pre>{@code
BlockingWebClient client = BlockingWebClient.of("https://api.example.com");
ResponseEntity<String> response = client.prepare()
                                        .get("/v1/items/1")
                                        .asString()
                                        .execute();
}</pre>
core/src/main/java/com/linecorp/armeria/client/BlockingWebClientRequestPreparation.java