[new] add show-result-list for confusion_matrix

Description：允许confusion_matrix使用者传入标签参数 Main reason: 便于confusion_matrix提取指定的label

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[x] The PR title starts with [$CATEGORY] (例如[bugfix]修复bug，[new]添加新功能，[test]修改测试，[rm]删除旧代码)
[x] Changes are complete (i.e. I finished coding on this PR) 修改完成才提PR
[x] All changes have test coverage 修改的部分顺利通过测试。对于fastnlp/fastnlp/的修改，测试代码必须提供在fastnlp/test/。
[x] Code is well-documented 注释写好，API文档会从注释中抽取
[x] To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change 修改导致例子或tutorial有变化，请找核心开发人员

Changes: 逐项描述修改的内容为ConfusionMatrix类增加show_result属性，ConfusionMatrixMetric修改为使用修改后的ConfusionMatrix类

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@修改过这个文件的人 @核心开发人员

fastnlp / fastNLP