static ResponseLogLevelMapper of(LogLevel successfulResponseLogLevel, LogLevel failureResponseLogLevel) {
        return log -> isSuccess(log) ? successfulResponseLogLevel : failureResponseLogLevel;
    }
Returns the default {@link ResponseLogLevelMapper} which returns the specified
{@code successfulResponseLogLevel} when logging successful responses (e.g., no unhandled exception) and
{@code failureResponseLogLevel} if failure.
core/src/main/java/com/linecorp/armeria/common/logging/ResponseLogLevelMapper.java