请在sankey图中增加edgeLabel

[brianjojoray]

What problem does this feature solve?

sankey图中没有edgeLabel属性，我希望可以增加此属性。
效果：
edgeLabel可以配置为显示，或者高亮时显示。

What does the proposed API look like?

参考graph关系图中的edgeLabel

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[github-actions]

This issue has been automatically marked as stale because it did not have recent activity. It will be closed in 7 days if no further activity occurs. If you wish not to mark it as stale, please leave a comment in this issue.

[github-actions]

This issue has been automatically closed because it did not have recent activity. If this remains to be a problem with the latest version of Apache ECharts, please open a new issue and link this to it. Thanks!