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

[francoisledroff]

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 .envfile and the metadata in a.aio` file