public ClientFactoryBuilder useHttp2Preface(boolean useHttp2Preface) {
        option(ClientFactoryOptions.USE_HTTP2_PREFACE, useHttp2Preface);
        return this;
    }
Sets whether to send an HTTP/2 preface string instead of an HTTP/1 upgrade request to negotiate
the protocol version of a cleartext HTTP connection.
core/src/main/java/com/linecorp/armeria/client/ClientFactoryBuilder.java