Export: Add kind=Sidewalk to hw=path that we understand to be a sidewalk

Maybe related to #65

To my understanding the System already know that this `hw=path` is a sidepath, even though it is not tagged as such.
However, when exporting, we cannot filter it this way. I get the `kind=Sidewalk` on the generated ways, but not on those that we recognized as such.

https://a-b-street.github.io/speedwalk/#19/52.763256/13.244696

I expected the kind=Sidewalk on the `highway=path` but it its `kind=Other`.

这个 issue 涉及导出逻辑未为已识别的人行道路径分配 `kind=Sidewalk`。查看处理 OSM 数据导入和分类的代码，可能位于处理 `highway=path` 标签的模块中。找到人行道检测发生的位置，以及生成导出标签的位置。查看链接的 issue #65 以了解上下文。目标是确保被识别为人行道的导出 ways 获得正确的 `kind` 标签。

由索引模型根据 Issue 内容生成。