Custom devcontainer folder name when developing features locally

I am exploring the idea of using a `devcontainer` as a portable toolbox. The main idea is to have a repo that just constitutes what would be the usual `.devcontainer` folder. The problem is that I do not want to use that name, to not clash with that name if the project I use it within is already using devcontainers.

The idea is that through locally developed features, I could create a number of scripts (e.g., local `uv` tools) that I can just use within any project (and benefit of the ease of mounting of devcontainers).

All works really well, and I am happy where this is going, but the main problem is that to reference a feature that lives locally, I must have a `.devcontainer` folder. For the rest, I can call the folder whatever I want and just pass a `--config` flag.

Is there any chance where that constraint is removed and locally referenced features work in any arbitrary folder? Maybe the parent folder of where `--config` is pointing to?

首先跟踪 CLI 对 --config 的处理，以及解析本地引用 feature 的代码。检查当前如何强制执行 .devcontainer 要求，以及相关测试是否覆盖任意配置位置。完成标准是：本地引用的 feature 可以从任意文件夹运行，而不要求使用 .devcontainer 这个名称。

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