import: allows to download/copy also files that are not output

[Baranowski]

Documentation update necessary after PR treeverse/dvc#2889 for issue treeverse/dvc#2862

I will do this

[shcheklein]

thanks @Baranowski 🙏

[Baranowski]

I'm planning to do this after the corresponding dvc PR is accepted, or at least when it's close to being accepted. Just to avoid back-and-forth if there are changes in the supported functionality.

If you prefer me to write the docs update right away, please let me know.

[shcheklein]

@Baranowski sounds like a plan to me! No need to push it ahead of time.