[漏斗图] 暴露转化率给用户

[liuzhenying]

PR includes

• fixed #0
• add / modify test cases
• documents, demos

暴露 FUNNEL_CONVERSATION 变量，同时规范并修复使用此变量的 demo

[github-actions]

😭 Deploy PR Preview 5d79ef2 failed. Build logs

_{🤖 By surge-preview}

[coveralls]

Pull Request Test Coverage Report for Build 452224209

• 4 of 4 (100.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 96.773%

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Files with Coverage Reduction	New Missed Lines	%
src/utils/transform/word-cloud.ts	1	97.75%

Totals
Change from base Build 450830519:	-0.03%
Covered Lines:	4411
Relevant Lines:	4449

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💛 - Coveralls

[hustcc]

@liuzhenying 暴露图表内部的字段名称，迟早的事情，漏斗图第一个来搞，点赞。

但是建议不是以 static 属性的方式，而是直接 export 吧，可以做一个规范，比如：${plotType}_${fieldName}_FIELD。

对于这个，其他同学看有没有一些想法，这个迟早要处理了。

[hustcc]

决定方案：

1. 直接 export 变量
2. 规范： ${plotType}_${fieldName}_FIELD (全大写)