`core`: streamline the Workspace creation by using the Adobe Developer Console `project download` file

Ideally the Workspace creation should not involve manual copy and paste
we should take a similar approach as in the nodejs `aio-lib-* project
see https://github.com/adobe/aio-cli-plugin-app/blob/7.0.1/src/lib/import.js#L596
see https://www.adobe.io/apis/experienceplatform/project-firefly/docs.html#!AdobeDocs/project-firefly/master/getting_started/first_app.md
and segregate the secrets in an `.env` file and the metadata in a `.aio` file

首先阅读 src/lib/import.js 中引用的 nodejs 实现，以及链接的 Firefly 入门文档，以了解项目下载格式。当创建 Workspace 不再需要手动复制和粘贴，并且将 secrets 分离到 .env、将 metadata 分离到 .aio 文件中时，即表示完成。

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