provide (historical) tar archives for each ET release

Issue #2673 new
Roland Haas created an issue

A while ago in a ET call we concluded that it would be good to provide tar files of a full ET checkout (no version control metadata) for each release. This is useful in case repository servers referred to in thornlists go away.

Roland has copies of most releases and should be able to provide tar files.

For upcoming release we could also include the tar files as downloadable “deposits” in the Zenodo publication https://doi.org/10.5281/zenodo.3350841 This is nice to have an external hoster that should be around for a long time, but adds extra complications for the release process since one must create the tarball-to-be-deposited (incl. einsteintoolkit.bib which points to the Zenodo entry) before the release and before the Zenodo entry is published (similar to Description.md).