Declare `kaleido` as an optional dependency

When calling write_image on a figure, it is required that kaleido is installed in the active environment. It would be great if this dependency were declared in pyproject.toml as an optional group.

For example, here is the approach taken in pyvista:

https://github.com/pyvista/pyvista/blob/e1401a34cbd281bbe74bce8dccbb78b85ab36dc4/pyproject.toml#L40-L59

This would improve ergonomics for packages that depend on plotly, since kaleido is (from their perspective) an implementation detail. Such a package could then depend on plotly[io], for example.

从 pyproject.toml 开始，将其可选依赖配置与链接的 PyVista 示例进行比较。在一个可选组中声明 kaleido，使软件包可以依赖 plotly[io]，然后验证依赖元数据是否正确公开了该 extra。