`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

Start by reading the referenced nodejs implementation in src/lib/import.js and the linked Firefly getting-started documentation to understand the project download format. Done should mean Workspace creation no longer requires manual copy and paste, with secrets separated into .env and metadata into .aio files.

Written by the indexing model from the issue text.