public void addAttribute(String alias, AttributeKey<?> attrKey, Function<?, String> stringifier) {
        ensureNotStarted();
        requireNonNull(alias, "alias");
        requireNonNull(attrKey, "attrKey");
        requireNonNull(stringifier, "stringifier");
        configureExporter(builder -> builder.attr(alias, attrKey, stringifier));
    }
Adds the specified {@link AttributeKey} to the export list.

@param alias the alias of the attribute to export
@param attrKey the key of the attribute to export
@param stringifier the {@link Function} that converts the attribute value into a {@link String}
logback/logback12/src/main/java/com/linecorp/armeria/common/logback/RequestContextExportingAppender.java