如何使用图片来设置自定义图例？

[jiw29]

• [ ] I have searched the issues of this repository and believe that this is not a duplicate.

Reproduction link

https://f2.antv.vision/zh/examples/component/legend#marker

Steps to reproduce

对于这个例子，如何使用自定义图片作为图例呢？

Environment	Info
f2	3.8.7
System	-
Browser	-