@UnstableApi
    public static ResponseTimeoutMode responseTimeoutMode() {
        return RESPONSE_TIMEOUT_MODE;
    }
Returns the {@link ResponseTimeoutMode} which determines when a response timeout
will start to be scheduled.

<p>The default value of this flag is {@link ResponseTimeoutMode#REQUEST_SENT}. Specify the
{@code -Dcom.linecorp.armeria.responseTimeoutMode=ResponseTimeoutMode} JVM option to
override the default value.

@see ResponseTimeoutMode
core/src/main/java/com/linecorp/armeria/common/Flags.java