Academy: Set up workflow to import issues from participating projects

While this is a central repository for the Open Documentation Academy, documentation issues are likely (and properly) recorded directly in other repositories. However, for ease of use and visibility, these issues should also exist in the ODA.

There should be an established, automated and obvious way (e.g. by adding a label) to get issues included here

Possible solution: an action in each participating repo which picks up on a unique label, similar to https://github.com/marketplace/actions/github-issue-copier